Re-organize media files and add simplified Yo wordmark

- Better organization of media -- source/ for vector source files, and
  optimized/ for files created from source files.
- Split character file into individual files with proper names
- Remove old unreferenced source files that aren't our responsibility to
  maintain
- Add simplified Yo wordmark
Merge pull request #127 from robwierzbowski/rw/yo-mark

Re-organize media files and add simplified Yo wordmark