Update Readme.md to use relative links

https://help.github.com/articles/relative-links-in-readmes
Merge pull request #45 from vBm/patch-1

Update Readme.md to use relative links
use the _countof macro when it makes sense to do so
libmpeg2.cpp: disable C4244 for x64
update Little CMS (git ff060c3)
update Changelog.txt
update VirtualDub to v1.10.4-test1
require Inno Setup v5.5.3
update Inno Setup Basque translation