Windows port of Graphite

Port of Graphite to Windows using help from Ron Cordell.

Port is based on extracting all platform-specific code to a new file called crossplatform.py and replacing all platform specific invocations in the lib directory by calls to crossplatform functions.

I hope that the usage of platform.system() is fine from a performance point of view.

Missing in this port is the adoption of setup.cfg where the prefix needs to be changed for Windows.