Fixed build scripts, added elixir icon, regenerated font.

I've refactored the build scripts and managed to get a reproducible build working on OSX.

I haven't tested it on linux yet. Will check it on Ubuntu next up.

Added the elixir icon. It was easy once I had the original SVG icon files you used to make the font.

The scripts have all been moved into the `src` directory, where they build the font, then if all goes okay they replace them in the parent directory.

The only thing I couldn't get working was the `create-css-fixes.py` script, but as that seemed to generate something for the mfizz website, which I didn't have any info about, I commented it out for the moment. If you want me to fix that, I'm happy to, but I kinda need to know what it's supposed to be producing.

Along the way, I noticed that there aren't icons for EOT, TrueType, WOFF and SVG, so I guess I should make some of those next. :-)