avoid dereferencing a nullptr object

See merge request !276

MSVC minimum version and clang identification

See merge request jvet/VVCSoftware_VTM!277

Update ALF syntax element with specification

See merge request jvet/VVCSoftware_VTM!278

- fail to build when MSVC version too low
- properly identify clang as compiler

Dereferencing a nullptr should be avoided, even if the passed object is never used.
It may not be the most elegant solution to pass an empty list object, but it should work.

enable JVET-L0283 MRLP

See merge request jvet/VVCSoftware_VTM!272

Fix ticket #177 on encoder decoder mismatch for VTM-4.0rc1

See merge request jvet/VVCSoftware_VTM!273

IBC block search history status is not reset for each frame, which may affect IBC searching results for the second frame.

Compiling error fix in IntraPrediction.cpp when JVET_M0102_INTRA_SUBPARTITIONS is disabled

See merge request jvet/VVCSoftware_VTM!270

SW and spec mismatch related to wide angle #174

See merge request jvet/VVCSoftware_VTM!260

remove SPSNext extension and sort SPS

See merge request jvet/VVCSoftware_VTM!268

- all elements of SPSNext are moved into SPS
- syntax elements of SPS are sorted according to draft (as far as possible)
- comments were added where software and draft diverge

fix typo in tracing code

See merge request jvet/VVCSoftware_VTM!267

fix IBC indication in reshaper and hash ME

See merge request jvet/VVCSoftware_VTM!262

fix ENABLE_TRACING build

See merge request jvet/VVCSoftware_VTM!264

Keep align syntax-element variable with trace

See merge request jvet/VVCSoftware_VTM!261

- fix block statistics code for IBC mode after JVET_M0483_IBC
- enable build of block statistics code, when ENABLE_TRACING is specified on the command line

- removes old getIBCMode functions from SPSNext
- fixes references to this function in
  * reshaper
  * hash based ME

Note: SPSNext is going to be removed. Fixes can also be applied with the removal patch.

Clean up scan data arrays

See merge request jvet/VVCSoftware_VTM!257

Fix spaces and indentation in CabacReader

See merge request jvet/VVCSoftware_VTM!259

Remove outdated macros and associated code

See merge request jvet/VVCSoftware_VTM!258

Remove JEM_USE_INTRA_BOUNDARY and HEVC_USE_4x4_DSTVII

Use a single array with elements that comprise scan x position, y
position, and index into block instead of separate arrays.

Simplify array initialization code

Align ALF trace with specification

See merge request jvet/VVCSoftware_VTM!255

Cleanup CABAC contexts

See merge request jvet/VVCSoftware_VTM!253

Remove unused variables / declarations

See merge request jvet/VVCSoftware_VTM!254

Remove unused contexts and split intra mode contexts into luma and
chroma sets to align with text description

Update the software documentation/manual for VTM/JVET

See merge request !252

- change README.txt to markdown (displays in GitLab)
- update build instructions
- update LaTEX document template for JVET and include it
- general updates for the software manual (authors, purpose, etc.)
- update build instructions (aligned with README)
- use code highlighting (requires Pygments installation)
- minor formatting updates