Revert "Use an ActiveRecord model to manage checksum cache"

Unfortunately, it seems difficult to attach ActiveRecord::Base objects
to different connection objects. This will be needed to implement a
feature shortly which preserves views created within transactions.

This reverts commit 3e22f9853ce82205a01d6dd485789ddf5458998a.

Conflicts:
	lib/active_record_views/checksum_cache.rb
	spec/active_record_views_extension_spec.rb
Ignore surrounding whitespace when retrieving view SQL
Create views outside of transactions to ensure they don't rollback

Fix fixes views disappearing between tests using transactional fixtures
when running with application preloaders like Zeus.

Fixes #3
Bump version