Feature: accept regular expression matching

[mingard]

Overview

For more specific route matching, this PR introduces a basic regex match execution.

Example
paginated posts: posts/:page?[^\d+$]
single post: posts/:title?

This is only an interim measure to satisfy a project requirement, so I'm open to suggestions.

[developit]

Might have odd interplay with the match ordering from #136

[mingard]

@developit I'll run some tests. It could prove benificial to introduce some acceptance tests ontop of the current unit tests.