Adding support for DataMapper

Basically we had to change every usage of

ActiveRecord::Base.connection
to use the new abstraction we created.

This led to more problems than expected when dealing with threading issues and connection availability to each thread.
Merge pull request #24 from soundcloud/datamapper

Adding support for DataMapper
bumping version.
Merge pull request #25 from soundcloud/datamapper

bumping to version 1.2.0
updated the changelog with info for 1.2.0.
Changed the code slightly to handle different dm versions.
be more explicit about the default table switcher strategy.
Merge pull request #26 from kickstarter/docs_update

Be more explicit about the default table switcher strategy.
Update changelog
Revert "Merge pull request #25 from soundcloud/datamapper"

This reverts commit 97a6f78c758296be15e7d9d80cfb7754536f72ec, reversing
changes made to dcf23359a1841e39a30758984a2074c6dc0ed523.
Update copyright notice
Bump to 1.2.0
limit table name to 64 characters
Mention Primary Key requirement
add spec
Merge pull request #28 from charliesome/cap-table-name-at-64-chars

Limit table name to 64 characters in length
Lhm.cleanup method
Merge pull request #29 from bogdan/master

Lhm.cleanup method
Update changelog
Bump to 1.3.0