Integration with Devel Generate

This covers a reasonable amount of functionality.

I decided to commit this (with a tweak to the README.txt) as it'll help with other issues, particularly #1572474: Add Revisions to Metatags for Entities.

I've changed to logic so it's configurable as to how many meta tags will be given a value, rather than hardcoding it.

This version extends #4 by adding phone number support.

This updated patch covers all of the meta tags except for date fields.

Committed. Now on to the fun issues.