WIP: Text

WIP. Before merge, need to add tests.

Currently working:

1. Calculation (Cython) and utilization of SDF.

2. Linux text display and system font listing.

3. OSX text display and system font listing.

4. Win32 text display and system font listing.

5. Automatic downloading of a couple nice open-source fonts.

6. Make it a `Visual`.
mmm... that makes sense. Somehow I was under the impression that all glyphs got the same size. Sorry for the noise.