lavr: fix mixing matrix reduction when normalization is disabled

In some cases when an input can contribute fully to the corresponding output, other inputs may also contribute to the same output. This is the case, for example, for the default 5.1 to stereo downmix matrix without normalization.
Fixed incorrect CBaseSplitterFile::BitRead function on x64.
Fixed potentially incorrect work of function CGolombBuffer::BitRead.
CONTRIBUTING.md: update trac's url
installer: update Armenian translation
batch files: always switch to the batch file dir first, add license headers in the translation helper scripts
vsfilter_setup.iss: bump minimum Inno Setup to v5.5.3
Compilation.txt: update msysgit version
update ffmpeg (n0.8-18583-g911e270)
update docs/Release.txt