Add CrxDecompressor for CR3 raw files

This decompressor is ported from libraw. Some of the file handling logic
has been replaced by rawspeed::Buffer and derived classes.
Most of the code is untouched.

Author: cytrinox

src/librawspeed/decompressors/CMakeLists.txt

@@ -11,6 +11,8 @@ FILE(GLOB SOURCES
   "Cr2Decompressor.h"
   "CrwDecompressor.cpp"
   "CrwDecompressor.h"
+  "CrxDecompressor.cpp"
+  "CrxDecompressor.h"
   "DeflateDecompressor.cpp"
   "DeflateDecompressor.h"
   "FujiDecompressor.cpp"