Update to static plugin

An update to the static file server plugin that addresses issues found in

https://github.com/mcavage/node-restify/issues/420

as well as updates to the documentation and tests related to the issue.

This updates the behavior for static file serving to use more intuitive
directory linking where /some/path/ can easily be mapped to /another/place/
including all subdirectories.
#420 - Static plugin repair.
Merge pull request #451 from JasonGhent/master

Update to static file server plugin