Add test for concat into dataframe
Take advantage of pandas concat
Merge pull request #665 from cpcloud/speedup-concat

Take advantage of pandas.concat
mongo post_compute robust to missing keys

Use pluck(default=None)
Add a test for rowwise groupby
Allow rowwise in get_grouper
Merge pull request #673 from cpcloud/pandas-by-rowwise-fix

Fix rowwise groupby in pandas
Merge pull request #669 from mrocklin/mongo-robust-to-missing-values

mongo post_compute robust to missing keys
Discover for Series
Add tests for attributes
Add test for Attribute Expression repr
Implement Attribute expression
Implement compute_up for pandas + Attribute
Spurious import
Add tests for python backend
Implement Python backend
Add millisecond
Add mongo tests
Implement mongo
Implement millisecond for pandas