MediaFormats: Exclude non-associable formats from the search for supported extensions unless specified.

Fixes #3091
MediaFormats: Write fAssoc variable name in full. (Cosmetic)
CFileAssoc: Prevent non-associable formats from being registered.
Use nullptr instead of NULL whenever possible.

Microsoft recommends to avoid using NULL or zero (0) as a null pointer constant since nullptr is less vulnerable to misuse and works better in most situations.

Also fix some cases where NULL was used instead of 0 or FALSE.
Cosmetics: Use IsEmpty() instead of comparing with the empty string.
Cosmetics: Use short aliases for AfxGetAppSettings() and AfxGetMyApp().
Cosmetics: Remove extra parenthesis.
Cosmetic: Add parenthesis to make a test obvious.
AviSplitter: improved playback for non interleaved AVI files, reduced memory usage, "Non interleaved files support" option is always enabled now.
VSFilter: move the version to a separate file.
AboutDlg.cpp: use the MPC_VERSION_ARCH define
Using a precommit script seems like speaking Chinese for some.
setup WIP
Rename the CRenderersSettings variable for consistency.
Simplify preprocessor config.
Constify CRenderersData when possible.
Constify GetPerfCounter().
Cosmetics: move variable declaration to the same line it's assigned.
Rename variable for consistency.
update Changelog.txt