Add Mercurial, add uninstaller for msysgit, add MS Web Platform Installer v5.0

Both 32-bit and 64-bit MSI packages included for Mercurial and MS Web PI.

I guess 32 bit windows is quite rare now (especially server side since 2008 was the last 32-bit server OS), but I hope this ad hoc convention of "foo_x86" and "foo_x64" is reasonable.