Adds selecting which warning to turn into error
Adds selecting which warning to turn into error

This is helpful when you only want a particular class of warnings to be turned
into errors.

If the warning of interest is one of the standard python ones
(https://docs.python.org/3.1/library/warnings.html) you can pass to nosetests
only the warning class name, eg: `--warning-class=Warning`

For anything else provide the full Python path:
`--warning-class=package.module.CustomWarning`

Bernhard10/WarnAsError