Minor Refactoring of indexer.series_indexer()

In commit 520f3ef423fa20cbe76851a14dfadc314c3e6f4b, I removed the need
for this call to Series.__init__(), but I didn't remove the call to
Series.__init__(). So now I did.

Further, series_indexer() never needed a "types" parameter, so it's gone.
Updated indexer.Indexer to Use MPInterface

Also updated tests. Updated actual indexers and tests are forthcoming.
Revise the run_tests.py File (Cleaned the Imports)
Update indexers.template.indexer_func() Documentation to Help Subclassing

Inspired by A. Morgan.