refactor wait for values

• numeric values now tolerate some defined lack of precision that would be apparent in floating point numbers
• wait for only returns the value, no longer has the timer in-built in the method
• each time a keyword is executed and passes, the elapsed time is set to a KEYWORD_DURATION suite variable accessible in robot framework

New

• float comparison more generalised and doesn't use equality
• get values and wait for values are casted to the appropriate type before being returned
• booleans handled more thoroughly, can use RFW boolean types or string bools (literally a string of False/false)
• More through testing of the refactored wait for value method
• Robot Framework listener reports keyword duration of only specified keywords