Add 'named callable' rules to Form validation library

Requested in issue #3183
Supersedes PR #3220
Add svg to config/mimes.php

Close #3199
Added vcard mime-type
Merge pull request #3229 from aanbar/add_vcard_to_mime

Added vcard mime-type
Fix #3228
Merge branch 'develop' of git://github.com/EllisLab/CodeIgniter into develop

Conflicts:
	user_guide_src/source/libraries/form_validation.rst