Add stateful apply to algebra
Sphinx style documentation for applies
Better name for updater expressions variable
Allow evaluation of expressions with state
Add stateful apply to myrialang
Simple test for stateful apply
Fix typo in comment
Cleanup test and better naming of test case
Test running average using stateful apply
Call iter expressions emit expressions, change order of update and emit in stateful apply, state is a relation with a schema
Add test for proposed language extension for stateful applies
Rename mapping to emitters in constructor as was done at other places, make state a named tuple
Add Cast and Type expression operators
Remove test for running mean until we have decided what the language will look like.
Clean up imports
Fix type expression
Merge remote-tracking branch 'origin/master' into domoritz-stateful-apply

Conflicts:
	raco/myrial/groupby.py
Fix merge
Add test for cast to float
myrialang: throw an error when an invalid raw query is submitted

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>