Separated split_by() from split_at()
Added coverage build mode to docs Makefile

Useless though, wrong structure of docs.
Renamed groupby() to group_by() for consistency

To be consistent with split_by() and potential partition_by() to be exact
Added mro by hand example
Updated version to 0.3 in docs

They gone too far from last 0.2.1 release
Completed seqs docs
Renamed argument of split_at() from pos to n