Changes:
- introduced compatibility with Visual C++ 2010 and newer
- attached Visual Studio 2010 project
- thoroughly tested with 21 Travis CI and 7 AppVeyor CI tests
- fixed bug with reusing a context in lz5frame.c (LZ5F_compressBegin and LZ5_compress_HC_continue)
- fixed rare bug in match finder (concerns levels 4 - 15)