Add an error check for trying to interact with expired subtitles objects
Use boost.interprocess's mmap wrapper in the PCM provider
Extract the rest of the mmap logic from the PCM provider. Closes #934.
Use read_file_mapping directly in the HD audio provider
Use mmap for reading subtitles from Matroska files

Cuts cold-cache read time for an arbitrary 1 GB file read over a network
off a USB 2.0 hard drive from ~70 seconds to ~45 seconds.
Fix crash_writer_minidump.cpp's newlines
Simplify PCMAudioProvider a bit and pull it fully into the cpp file
Remove unused variable