Provide support for x64 builds in Visual C++ project files.

* src/builds/win32: Renamed to...
* src/builds/windows: This.

* src/builds/windows/vc2010/*: Updated to handle x64 target.

* src/builds/windows/*.mk, docs/INSTALL.GNU: s/win32/windows/ where
appropriate.
Comment on no-stem-darkening & darkening-parameters
Provide cmake support.

* CMakeLists.txt: New file.
* README.git, docs/CHANGES, docs/INSTALL: Updated.