Moved index updating to the utils module. Added the signals module to
automatically connect to Django's `post_save` signals for indexed
models. Currently have an issue with testing: it seems like there's an
attempt to create th index twice. Must look into that, it's surely due
to these new additions.
Fixes #18 and #20. Can now automatically update index of models (if
requested in the settings). Also fixes double indexing bug of same
objects.
Merge pull request #21 from Sparrho/issue-18

Issues 18 and 20.