Update validate.js

Small changes to pass JSLint with default options: Removed a few stray colons, re-declared vars and un-escaped chars.
Updated the readme.
added valid_url validator
Only validate fields that actually exist
Changed a comment style.
Merge pull request #57 from tajo/master

Added url validator
Merged pull request #54 from i-like-robots.
Fixes issue #55 with code from jnhwkim.
Merge branch 'master' into gh-pages
Updated documentation for valid_url.
Added release notes for 1.2.1.
Upped verison number to 1.2.1.
Merge branch 'master' into gh-pages
Updated minified version to 1.2.1.