Added URL field. Optionally clears input if URL is invalid.
Added URL field, adds protocol and clears (overridable) input if URL is invalid.
Merge branch 'text_url' of github.com:dessibelle/Custom-Metaboxes-and-Fields-for-WordPress into text_url
require_valid defaults to true.
Added URL escaping.
Stripped custom logic/protocol identification to rely entirely on esc_url_raw().
Added protocols option to text_url field.
Merge pull request #350 from dessibelle/text_url

Added a URL field, props @dessibelle