These are shorthand for endogenous and exogenous variables. You might be more comfortable with the common y and X notation in linear models. Sometimes the endogenous variable y is called a dependent variable. Likewise, sometimes the exogenous variables X are called the independent variables. You can read about this in greater detail at endog, exog, what’s that?
Missing data can be handled via the missing keyword argument. Every model takes this keyword. You can find more information in the docstring of statsmodels.base.Model.
If you’re on Python 3.4, you must use Cython 0.20.1. If you’re still having problems, try running
python setup.py clean