Added all of alan's test cases
Tried to clean up test runner... a little
Fixed capital var error test

We previously considered a variable to be any character (lower or upper)
followed by zero or more characters and digits.

The specification calls for only a single lower case letter.  We
replaced our regex with the correct one here.
Added spaces around + before splitting

This was causing math_in_print to break.  The + sign was being thrown
out
Threw error on bad characters in string

There should be no non-lower-alpha (or space).

We now check for that in our string-replacement function
Added word error to certain tests
Revert "Threw error on bad characters in string"

This reverts commit 1f17333935d58dd0910494a8b1daaf7f5a6ed771.

Conflicts:
	lex.ml
Raised error on special characters in strings