Modify _url to use URI for standard encoding

HTTP::Tiny does not automatically encode the URL. This patch uses URI to form the URL correctly.
Passes back a URI object, which should stringify when the request is made.
Fix bug from updating FIELDS section

Misunderstood a line of code, rewritten to make it right.
Also put squiggles around a hashref :)
Merge branch 'm4ddav3-master'
- Merged patch from David-Kitcher Jones about using URI for url encoding.
- Added 'URI' as pre-requisite to the Makefile.PL file.
- Updated pod documents (fixed code).