style(parser): Improve RegEx for parsing chars.
test(parser): Better test description.
feat(mutation): Introduce mutations.

Mutations are a small helpers that define mutation functions. These
function will be used to transform HTML to Markdown and vice versa.
test(mutation): Remove ddescribe...
chore(grunt): Add mutation + parser to src files.
feat(mutation): Made the mutations more useful.

Changed the way mutations work. Instead of a function there is now a
"start" and "close" string that wraps around the content. This way the
mutations can be better used to transform small bits of HTML / Markdown.
feat(mutation): Shorthand when start and close are the same.

When start and close options are equal you can now omit the close
option. E.g. { exp: /i|em/, start: '*'}.