Changed Root's toString() method such that it doesn't display a <degree> prefix if the degree is 2. This matches the mapping to match expressions, where [root-symbol](something) is by default interpreted as a square root.
Changed the type of ExpressionParser to UTF-8.
Developed expression parser more (still incomplete). This is a very complex class that may need an external library if my current approach is too buggy (as I approached this with less up-front design and seriousness than I should have). It will also need some major refactoring afterward for understandability.