Add implementation section to README

This describes what is going on under the hood with an example query
generated using the API.
Abstract out SQL templates

All string formatting has been converted to the built-in 'advanced'
formatting present in 2.6+.

The true/false values have been removed from the case statement
construction since the values were constant across operators.
Remove legacy code and files, update LICENSE

These files are not longer necessary after the client was moved to
a separate repository.
Simplify ItemThroughManager manager methods

Previously, the `exclude_*` methods did not handle the actual
negation of the matched records. As a result, this was left up to the
client to handle which is clearly a broken implementation. This has
been fixed and propagated through out the tests and translator. This
is technically a breaking change, but the methods have not been
considered public API so it is unlikely client applications will be
affected.
Standardize tests layout, add Travis CI, update coveragerc