Add TreeMaps view of Unicode Blocks

[davelab6]

• [x] Rename ./coverage_pngs/ to pyfontaine-YYYY-MM-DD-HHSS
• [x] Rename --coverage to --show-hilbert and output PNGs to pyfontaine-YYYY-MM-DD-HHSS/$fontFileName-hilbert.png
• [ ] Add a --show-treemap-unicode that uses the matplotlib example http://wiki.scipy.org/Cookbook/Matplotlib/TreeMap by @jamescasbon (assuming the licensing is ok) to visualise each unicode character block that is touched by a font's character map, split between included and not included, and output PNGs to pyfontaine-YYYY-MM-DD-HHSS/$fontFileName-treemap-unicode.png
• [ ] Add a --show-treemap-sets that visualises each character set that is touched by a font's character map, split between included and not included, and output PNGs to pyfontaine-YYYY-MM-DD-HHSS/$fontFileName-treemap-unicode.png

[davelab6]

Example: a font is passed to pyfontaine with 3 charmaps, and it has 100% Adobe Latin 2, 76% Adobe Latin 3, and 30% gwf basic Cyrillic. A treemap result will have 3 cells, in 3 colours, one will be 'full', one will be 3/4 full and one will be 1/3 full.

However, I think this is better done live in browser with paper/two.js so it's interactive, so closing