Supplement the image code

* Fix some PHP error
* Add the various sizes that Twitter returns
* Link the URL in the tweet like other entities
* Clean up some code
Change version to '1.4.0'
Fix issue #18: regression on URL replacement

Because of a missing 'break', URLs would get replaced twice instead of
once, causing unsightly issues. This broke because of a change in version
1.4.
Change version to '1.4.1'
Add a note about support

Clarify what level of support we provide for this module (basically none), and our policy on the open source–ness of it.
Updated DB settings table name and incremented version.
Fixed version-check logic for 1.4.2 upgrade.