Unit test of stateful apply invocation
Add apply token to the scanner
Add brace characters to the scanner
Add apply to myrial grammer
Avoid keywords in apply unit test
Use stateful apply for bag comprehensions without aggregation
Turn dead code into an assertion in groupby.py
Register stateful apply functions into the myrial function table
Associate statemod varibles with emit arguments
Unpack state variables during UDF invocation
Export statemods through emitargs
Compile away unbox operations inside update expressions
Test of stateful apply with multiple invocations
Introduce name mangling to statemod variables
Merge from origin/master
Merge pull request #102 from uwescience/andrew_stateful_apply2

Expose stateful apply in Myrial
add sympy to auto-installable requirements
remove double call to compile_boolean in boolean_combine

compile_boolean() already is called in BinaryOp case.
Otherwise it messes up the visitor pattern.
boolean expression visitor and use it to refactor compile_boolean
undo 1bda0dd