reduce disk usage during write

[DanEngelbrecht]

• CHANGED API Longtail_StorageAPI.OpenAppend added to Longtail_StorageAPI to open files without truncating existing data
• CHANGED API Longtail_CreateConcurrentChunkWriteAPI changed to take source_version_index and version_diff
• CHANGED API Longtail_ConcurrentChunkWriteAPI refactored to use asset index and open/close files instead of keeping all open during entire lifetime
  • Longtail_ConcurrentChunkWriteAPI.CreateDir now takes asset index instead of version local path
  • Longtail_ConcurrentChunkWriteAPI.Open now takes asset index instead of version local path and dropping chunk_write_count parameter
  • Longtail_ConcurrentChunkWriteAPI.Write now takes asset index instead of version local path and dropping chunk_write_count parameter
• CHANGED API Longtail_SetMonitor callback functions refactored to accomodate changes in Longtail_ConcurrentChunkWriteAPI
• REMOVED API Remove platform api for Read/Write mutex
  • Longtail_GetRWLockSize
  • Longtail_CreateRWLock
  • Longtail_DeleteRWLock
  • Longtail_LockRWLockRead
  • Longtail_LockRWLockWrite
  • Longtail_UnlockRWLockRead
  • Longtail_UnlockRWLockWrite
• ADDED memtracer now tracks allocations in stb_ds
• ADDED memtracer now tracks allocations in zstd
• FIXED Fixed excessive "Disk Used" increase during Longtail_ChangeVersion2 execution causing Out Of Disk space errors.
  The changes also improves performance for more common cases with smaller archive sizes (60 Gb raw data/many files) but causes a small regression compared to 0.4.1 for archives with many very large files. It is still performing much more reasonable than 0.4.0 for these cases.

  Version	Files	Raw Size	Compressed Size	Unpack Time	Peak Memory
  0.4.0	1019	735 GB	214 GB	2h44m26s	7.9 GB
  0.4.1	1019	735 GB	214 GB	0h12m14s	1.9 GB
  0.4.2	1019	735 GB	214 GB	0h13m25s	2.2 GB
  0.4.0	239 340	60 GB	17 GB	0h01m24s	4.2 GB
  0.4.1	239 340	60 GB	17 GB	0h02m48s	0.9 GB
  0.4.2	239 340	60 GB	17 GB	0h01m12s	0.9 GB