Implement date field extraction.
Add array length operation

Postgres supports multidimensional arrays, so `array_length` takes a second parameter for the dimension. This currently only generates a plan when the dimension is 1. We could approximate higher dimensions by returning maybe the length of the largest sub-array at the appropriate depth.
Connect conditionals to Mongo.
Rename `Time` to `Temporal`.
Fix a non-exhaustive match.
Merge pull request #119 from sellout/63-additional-operators

More operations