Writes tests for custom defined errors of tardis/util.py
Writes tests for custom defined errors of tardis/util.py

- Three new methods introduced in test_util.py, of
  them the first method tests MalformedSpeciesError,
  second method tests MalformedElementsSymbolError,
  third method tests MalformedQuantityError.

- All 3 classes inherit from an empty MalformedError
  so MalformedError itself does not need unit test.

orbitfold/tardis,orbitfold/tardis,kaushik94/tardis,kaushik94/tardis,orbitfold/tardis,kaushik94/tardis,kaushik94/tardis,orbitfold/tardis