Modify scanner.jl to remove contains

Remove all contains errors, swapping with in. Running test suite with
just these changes doesn't appear to cause any additional errors.
Modified parser.jl to remove contains errors

Modified all functions using contains, replacing with in. After running
test suite, doesn't seem to be generating any new errors.
Modified to remove contains

Removed contains, substituted in function. No additional errors seem to
be generated running test suite
Fix add! error

Replaced add! with push!
Account for NaN inequality in tests.
Add LICENSE.md