@richardartoul @quackingduck FYI

Fixes #31 and #42 and should resolve #44

This PR:

• Enables literate javascript using javascript block comments
• Cleans up the literate code parsing logic overall to make it easier to add future languages
• Adds a new plugin to enable demarkation of language-specific blocks of text which themselves contain markdown (the crux of Experiment with adding more JS translations of the python source examples #44)
• Adds @richardartoul 's code for anagrams.js