This commit allows the attribute codec to be parametrised by attribute
bitdepth.  The attribute bitdepth is signalled in the attribute's sequence
parameter set description.  The specified bitdepth affects cliping in the
attribute prediction and reconstruction process.

This commit allows individual payloads to be inserted into the decoder
rather than the decoder expecting to decode each payload in a fixed
order.

When an output pointcloud is ready, the decoder will call a user
supplied callback with the conforming output pointcloud.  The user
may choose to rescale this point cloud as necessary.

This commit removes the "lossless" geometry bypass coding mode that simply
skipped coding of geometry and required the decoder to read the geometry
from the source video.  Bypass coding mode is replaced by octree coding.

This commit rewrites the codec high-level syntax:

 - the bitstream is divided into "bricks" (akin to an AVC/HEVC
   slice/tile).

 - sequence, geometry and attribute parameter sets describe the coding
   parameters in use generally and for a specific brick.

 - marshalling the bitstream payloads to a file format is achieved using
   a type-length-value encoding scheme.

Additionally, the triSoup bitstream scale and translation values have
been unified with (replaced by) the octree counterparts.  For
compatibility, existing command line parameters continue to function
as before.

NB: this commit does not incorporate flexibility in the decoding order.
The decoder requires the bitstream to be presented in a fixed order.

Khaled Mammou authored Jun 30, 2018 and David Flynn committed Aug 20, 2018

Point positions are represented at integer precision.  This commit
removes the need to perform an epsilon comparison when comparing
floating point positions.

The IntegerLift name is misleading in light of a separate coding method
that uses lifting predict and update operators.  This commit renames
the method to specify it is a prediction-only scheme.

Khaled Mammou authored Jun 30, 2018 and David Flynn committed Aug 20, 2018

This commit implements a lifting scheme optimized for lossy attribute
compression, consisting of predict/update operators, and an adaptive
quantization strategy.

Khaled Mammou authored Jun 30, 2018 and David Flynn committed Aug 20, 2018

Adaptively pick the number of neighbours considered during the
prediction based on analysis of the reconstructed attribute values of
the neighbours.

From m42642, this is performed by computing the maximum difference
between any two reconstructed attribute values of a points neighbours.
If the variability is higher than a threshold, then apply a
rate-distortion optimization procedure to choose between using either
a single neighbour or all neighbours. The index of the best prediction
strategy is arithmetically encoded.

This commit:
 - implements the m42642 method
 - moves buildPredictors into transform-specific attribute encoding/decoding
 - adds quantizationStepsChroma
 - renames quantizationSteps -> quantizationStepsLuma

df: fixed incorrect application of quantizationStepsLuma|Chroma
df: updated cat3 cfg to specify quantizationStepsChroma
df: fixed header encoding if quantizationStepsChroma missing

This commit removes the searchRange option that was set to 0 by m42538.

In the contextualisation of occupancy coding using neighbour patterns,
this commit replaces the case when neighbour contextualisation is
disabled with a constraint that restricts neighbour contextualisation
only examine the direct siblings of a node.

The restriction ensures that at most three neighbours may be present
for a node.

The configuration option "neighbourContextualisation=1" is replaced with
"neighbourContextRestriction=0".

This commit provides an implementation of m42522 to code occupancy
using a binary context model rather than a 255-ary model.  A total of
581 binary contexts are used compared to the previous 10 255-ary
contexts.

This commit removes the bundled Intel Threading Building Blocks library
from the repository.

This commit adds support for setting encflags, decflags and pcerrorflags
at the top-level of the config which are then applied to all categories.
Precedence is such that global enc/dec/pcerror flags are set after all
other more-specific definitions.

The gen-cfg.pl tool permits the merging of yaml input prior to
generation of the derived configuration files.

This commit permits merging of existing arrays.  For example,
given the following input (in order):

 file a: "{ key: [a] }"
 file b: "{ key: [b] }"

The merged structure is { key: [a, b] }.

The provision of these configuration files causes confusion when they
are not kept in sync with the .yaml files -- either due to modification
of the .yaml files without regenerating the .cfg files, or due to
direct modification of the .cfg files themselves.

Please see cfg/README.md for further details on how to generate
configuration files for the encoder/decoder.

The original integration of IDCM implemented only the parent based
eligibility check of m42239 and erroneously omitted the six-neighbour
check.

This commit adds the six-neighbour check, making use of the neighbour
calculation from m42239 neighbour contextualised coding of occupancy.

This commit fixes a null pointer dereference in cases where no
reconstructed point cloud output is specified.

This commit makes gen-cfg understand a pcerrorflag value on a
per test category basis in the same way as enc|decflags.

This commit updates the master configuration files to support:

 - new test conditions for cat3 tests
 - existing conditions for cat1 tests (for use by tmc13)
 - updates enc/decflags to use recommended forms
 - integrates pcerror flags (per condition / sequence)
 - adds sequence databases describing source files, and source
   parameters that may be used by other scripts.

The ctc-category-map.csv file has been removed -- a new version can be
provided if necessary.

If there is an issue running one of the tmc1 blocks, terminate
the encoding immediately and report the error.

This commit aims to reduce te amount of copy+paste code used to
support the three different geometry coding modes by unifying them
into a single flow.

This commit adds a DecoderParameters struct to reduce the overhead of
adding extra parameters.