initial refactor
Merge pull request #48 from otaviojava/refactor_quantity

initial refactor
UNITSOFMEASUREMENT-71: Should we rename of(CharacterSequence) to
parse()? 

Task-Url: https://java.net/jira/browse/UNITSOFMEASUREMENT-71
UNITSOFMEASUREMENT-71: Should we rename of(CharacterSequence) to
parse()? 

Task-Url: https://java.net/jira/browse/UNITSOFMEASUREMENT-71
UNITSOFMEASUREMENT-67: Convenience Factory Methods for Quantity or Unit 

Task-Url: https://java.net/jira/browse/UNITSOFMEASUREMENT-67
UNITSOFMEASUREMENT-69: Rethink hierarchy (and possibly naming) of
Quantity and Measurement 

Task-Url: https://java.net/jira/browse/UNITSOFMEASUREMENT-69