Added typeToString() function
Added check before doing math on dimensions to make sure the units match.
Added the unit() function for changing the units on dimensions.
Moved value processing code into the value dir.
Added String and Number classes that extend Value.

Number related code moved to Number and Value is now an abstract class.
Updated Makefile to compile the files in the src/value/ directory
Renamed String and Number to StringValue and NumberValue.
Updates so everything compiles with value processing code in the
src/value/ dir.
Fixed tests.
Enabled the strings as a value.