* adds test_ucon.TestRatio

* adds initial Ratio implementation and updates Number so tests pass

* fixes typo in README

* adds bromine density test case for Ration multiplication

* adds test_ucon.TestNumber.test_as_ratio

* adds Number.as_ratio

* convers RuntimeErrors -> ValueErrors

* adds tests ensuring ValueErrors raised where expected

* adds assertions affirming comparison flexibility between Numbers and Ratios

* implements comparison flexibility between Numbers and Ratios

* fixes assertion in TestRatio.test___mul__ test

* updates Ratio.__mul__ implementation so test passes

* updates README

* classifes project as "Alpha" release in setup.py