Dataframe-friendly Numba decorators

- dataframe_vectorize -> @vectorize from numba for Dfs
- dataframe_guvectorize -> @guvectorize from numba for Dfs

adds numba to test environment
tests with py.test
remove test funtions from utils.py
assume puf2.csv is in current working directory for Travis CI
add @wraps decorator

- preserves function name and docstring
numba-ized SSBenefits calc
resolved conflicts in order to merge