Fix deprecation warnings with recent ffmpeg
Add missing virtual destructor for OptionMapperBase
Don't reuse audio resampling contexts

Reopening an already open context no longer works, and creating a new
one is simpler anyway.
Set resampling options on the correct context
Make indexes not arch-specific

The data in the index isn't inherently arch-specific in any way, and
writing the data structures in a portable format doesn't actually make
the reading and writing code much more complex, so there's no real
reason not to.

Closes #120.
Fix unimportant typo in comment
Don't write fields which don't apply to the current track type to the index

Bumps about 10% off the compressed size of the index of a totally
arbitary file I indexed.
Add a script to build dependencies on windows
Update changelog
Add links to the rendered documentation in the readme
Update source location in the API docs
Update building instructions in docs
Add missing include in vapoursource.cpp
Fix a few x64 warnings
Update .gitignore
Underpify ffmsindex.vcxproj a bit
Use the appropriate toolset for the current version of Visual Studio
Initialize more stuff in FFMS_Index's constructor
Fix loading Matroska index files on x64

OriginalPos is an unsigned integer of inconsistent size which can be
negative (due to being delta-coded), which makes the exact order of the
casts and manipulations very important.
Fix saving and loading audio indexes