(PE-5860) Add regex support to wrap-proxy

Modify wrap-proxy so that the proxied-path variable can be
either a string or a regular expression pattern.
(PE-5860) Modify regex matching

Modify regex matching so that only part of the uri of the
request need match the regex, and so that the part that matches
is the beginning of the request uri.
(PE-5860) Address PR comments

Remove capitalization of scheme in proxy test. Use `string?`
instead of `instance? String`.
(PE-5860) Ensure regex does not match entire URI

Ensure that regex only matches the beginning of a request URI
in the wrap-proxy function rather than the entire URI.
(PE-5860) Add new proxy-request function

Move logic from true branch in anonymous function in wrap-proxy
to a new function in common, proxy-request. Change all unused
instances of `req` in handlers defined in test files to `_`.
(PE-5860) Use not-empty instead of let block

Replace a let block in proxy-request with the not-empty function,
as the let block did the same thing as the not-empty function.
Merge pull request #13 from fpringvaldsen/PE-5860-regex

(PE-5860) Add regex support to wrap-proxy