create setup.py and make pip installable from github

[rlskoeser]

for now, let's make it pip installable from github — then if we want we can publish on pypi later on

• [x] basic setup.py file
• [x] update readme with instructions for installing from github
• [x] add dev/test dependencies as optional package in setup.py requirements
• [x] update readme with instructions for installing for local development
• [x] update unit test to install requirements the same way
• [x] #28

[rlskoeser]

completed in #27 and #49