Allow tools to use exsting configuration if found or provided.

[carlio]

For projects which already have configuration for various tools, prospector should use and prefer that. This is a more general version of #10.

This already happens for pep8, however, only if the files are in specified positions. There should be a command line option (--config-for-pep8=some/path) which allows extra places to be searched.

[mbertolacci]

This would be very useful for pylint because I would like to import our own pylint plugin. Or is there another way to do that?

[carlio]

Prospector will now use a .pylintrc file or pylintrc file if one is found in the directory that prospector is run from. If you need to, you can also explicitly specify it like:

prospector --pylint-config-file path/to/my/pylintrc

Note that if this is used, prospector's own opinions on what should be enabled/disabled are completely ignored!

[carlio]

@mbertolacci This should enable you to import plugins, let me know if it doesn't work!