Enhance issuefy to allow addition of custom fields

[lamahmud]

I have a bunch of custom fields (some of which are required). I'm comfortable with adding code to your issuefy.rb in order to handle the new fields but the issuefy.rb file isn't properly documented so I'm uncertain how you are identifying the correct database fields to insert data into. If you can let me know how that works, I'll be happy to help. Thanks!