Merge pull request #17 from Scotchester/master

Only add validated field to array if value was returned
Merge pull request #18 from Scotchester/master

Fix meta box display when 'howto' option not set
Merge pull request #19 from Scotchester/master

Stop showing Add a Link button when max is 1
Bug fix for editing existing links in link manager

The important thing is the jQuery selector change in line 26.

Before noticing the bug while creating the Offices post type, it worked
because we were getting lucky that the overall meta box name was the
same as the field name.

The other changes are just minor formatting cleanup.