Adds command-line switch to set custom language comment styles per-run
Adds note to README about --languages argument
Defer buildMatchers to configure call instead of in Commander parser func

This means using the languages option when calling Docco programmatically will
work properly.
Switch to accepting a .json file path as argument, instead of a specialised syntax
Removes a superfluously added blank line
Merge pull request #232 from 00Davo/languages-argument

Languages argument, from #231