Multiple versions

[wesleytodd]

Adds support for testing with multiple versions of path-to-regxp. Also adds some build stuff and standard formatting. I can do separate PRs for them if you would prefer that.

Reference: https://wesleytodd.github.io/express-route-tester/

[wesleytodd]

Ok, added some error handling because some inputs will cause path-to-regexp to throw and the version in express@4 can return number keys, so it crashed the escape function. All of that should be fixed, and I added new display for when the regexp compilation fails.

[rjmunro]

This is great work. Please can it be merged ASAP. Particularly that it defaults to the same version as express actually uses, and that it displays when the regex won't compile.