Consider adding support for arrays/regexps as Route paths

[fruchtose]

It looks like react-router's internal implementation relies on path-to-regexp to translate Route paths into regular expressions for matching URLs in matchPath. path-to-regexp currently allows the path argument to be a string, an array of strings, or a regular expression. Currently the docs specify that routing must be done with string paths.

I understand that exposing this implementation detail may not be ideal, but consider that Express supports regular expressions in routes and Koa's docs are transparent about its use of path-to-regexp.

[pshrmn]

This was discussed and rejected in #4551.