Add case statement to myrial grammer

Conflicts:
	raco/myrial/scanner.py
Add Case expression to raco
Add unit test of binary case statement
Fix variable dereference
Test of ternary case statement
Test of case statement with aggregate
to string method for case expression
JSON compilation of CASE expressions
Unit test that combines CASE expressions with unbox
Merge pull request #140 from uwescience/andrew_case_statement

Add case statement to Myrial