Add UDF to get a float from the integer/decimal/sign fields
Refactor utility methods to Utils and add test
Add getArgToFuncMapping() to UDF
Simplify UDF implementation thanks to getArgToFuncMapping()
toFloat() returns object, to allow null values
Fix uses of toFloat() when could get a null
Change getSign() to return null for invalid data and remove commented code
Add use to SignedDecimalToFloat() and UnsignedDecimalToFloat() to README