path: performance improvements on all platforms

This commit significantly improves performance of all path functions.

Optimization strategies include:
* Replacing regexps with manual parsers
* Avoiding unnecessary array creation (including split() + join())
* Returning earlier where possible to avoid unnecessary work
* Minimize unnecessary string creation and concatenations
* Combining string iterations

PR-URL: nodejs#5123
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: James M Snell <jasnell@gmail.com>