Upgrading to v0.0.6 - Changelog below

CHANGELOG:
- Add .rvmrc to .gitignore
- Add ability for adapter to override ActiveRecord::Base.connection
- Rename Default to DefaultAdapter.
- Add Sqlite3Adapter, which serves as a virtual DB adapter.
- Explicitly convert `@type` to a symbol when passed into
  `WraithDB::Column`
- Ensure a valid connection is available before attempting to load the
  schema in `WraithDB::Schema`
- Bump version to v0.0.6