(WIP) basic feature command

@evansde77 

Not sure what's the best way to go about testing this. Just have very basic commands to update local develop branch and create a new feature branch.
error here when I run feature command:

(venv)[16:24:47 cirrus] (feature-command) feature
Traceback (most recent call last):
  File "/Users/jordancounts/git/cirrus/venv/bin/feature", line 9, in <module>
    load_entry_point('cirrus==0.0.0', 'console_scripts', 'feature')()
  File "/Users/jordancounts/git/cirrus/src/cirrus/feature.py", line 22, in main
    checkout_and_pull(local_repo, DEVELOP_BRANCH)
  File "/Users/jordancounts/git/cirrus/src/cirrus/git_tools.py", line 28, in checkout_and_pull
    dev_branch = getattr(repo.heads, branch_from)
  File "/Users/jordancounts/git/cirrus/venv/lib/python2.7/site-packages/GitPython-0.3.2.RC1-py2.7.egg/git/util.py", line 612, in __getattr__
    return list.__getattribute__(self, attr)
AttributeError: 'IterableList' object has no attribute 'develop'