add groupbyadd groupby
add earlysafe. remove try-except blocks

This commit noticibly slows down tests.
condeseq uses lanyseq
remove bind and bindstar
remove isempty
rearrange code in core.py
section headers in core.py
move goals section above and/or section
goalexpand docstring
two typos
Merge pull request #14 from mrocklin/master

Improve readability of `core.py`