Fix Issue #163 Autolinker plugin incorrectly ignores URL fragment identifiers

Fix for issue [#163](https://github.com/LeaVerou/prism/issues/163) (and extras I found)
* Capture query string and document fragment in url regex
* If inserting to attr-value, need to match url-link first, otherwise query string '=' gets picked up as punctuation.
* Don't prepend "mailto:" if it's already there (e.g. inside an href)