refactor code to use cairo like show-glyphs
implement ability to generate PNGs

generated PNGs are direct copies of what the work-area of kernagic would
contain for the given font, with given parameters. Useful for some none-core
uses of kernagic, like rendering previews of a ufo file, or regression testing
kernagic itself.
ui: do not set font_path on widget; if none was passed in arguments
improve win32 build and docs

(the docs are in the Makefile)
add test framework
Add reference images
changed ui strings for different methods
do wordwrapping instead of char-wrapping
Make mingw32 build download its own dependencies
mingw32 build improvements