Extracted `node.nodeName.toLowerCase()` into a function `tag(node)` for readability.
Unifying tabReplace, useBR and classPrefix under options.
Restricting a set of languages used for auto detection. Both as a global option and as a parameter for `highlightAuto`.
Using Object.keys in a couple of places for readability.
Using `getLanguage` instead of `languages.hasOwnProperty` in `highlightAuto`.
Merge branch 'options'