TST: Test GEE with missing.
STY: Remove docstrings from tests
TST: Uncomment and fix original missing data tests
ENH: Handle missing for extra data with formulas
ENH: Workaround patsy NA handling. Closes #805.
TST: Regression test for ols formula and NA category
TST: Test that raise on NA with formula is possible
ENH: Allow raise on missing with formula
DOC: Add NA-handling and patsy to release notes.
Merge pull request #2034 from jseabold/fix-1877

ENH: Handle missing for extra data with formulas