parse_timedelta raises inconsistent errors for erroneous input

[mwysokin]

For erroneous input I'd expect that parse_timedelta would raise a ValueError like in the docs (https://tempora.readthedocs.io/en/latest/#tempora.parse_timedelta). However I was able to trigger different types of exceptions which makes it difficult to handle errors properly.

1. ValueError as expected:

>>> parse_timedelta("Matrix4")
ValueError: Unexpected 'Matrix'

2. TypeError

>>> parse_timedelta("12345Matrix")
TypeError: 'matrixs' is an invalid keyword argument for __new__()

3. UnboundLocalError

>>> parse_timedelta("MatrixFour")
UnboundLocalError: local variable 'match' referenced before assignment

Would it be possible to make the errors more consistent?