workbook or test case for TransientAsciiMetric

[rhiannonlynne]

Can I please task @fedhere or @svalenti with creating a notebook or test case for TransientAsciiMetric? I updated some code in the file to fix docstrings, fix PEP8 errors, and update some minor issues (for example, reading the ascii file once, during the init instead of at each slicePoint).
But I don't have a test case to make sure that everything still works.
A demo notebook in the science/Transients directory would be awesome.

[rhiannonlynne]

Workbook provided -thanks very much! More testing/updating of metric underway.