Add FrameL API for GWF I/O
This PR adds an API for FrameL, the Virgo-developed GWF I/O library, this is currently the only GWF API that builds and is distributed on Windows, so this change effectively adds support for (basic*) GWF reading on that platform.
*the FrameL python API is fairly minimal, so only reads one channel from one file at a time, and has no support for ADC scaling, etc.