Arguments/Configuration Refactor

[jayclassless]

In this PR I took the liberty to refactor how command line arguments are handled so that configuration for prospector can be specified from a .prospectorrc/setup.cfg/tox.ini file, PROSPECTOR_* environment variables, and/or command line arguments. Most of the heavy lifting in processing all these sources for configuration is handled by a library I've been working on called setoptconf. This new rig should support all the same options prospector has had (unless I missed something), with the exception of --path. It now takes paths as positional arguments (but currently only processes the first path specified).

I've also tweaked the setup.py so that the prospector script is created/installed via a console_script entry point, rather than maintaining a bin/prospector script separately.

[coveralls]

Coverage remained the same when pulling e25fa88 on jayclassless:config_refactor into d99ab6a on landscapeio:master.

[carlio]

Awesome stuff 👍

Does this library also allow you to load from config files in ~/.config?

[jayclassless]

Yea, it could pull from something in ~/.config. It's just matter of adding/modifying the sources used in prospector.config.build_default_sources(). Do you have a particular filename and/or format in mind?

[carlio]

No not particuarly, it's just something that I noticed other tools such as pep8 do - see https://github.com/jcrocholl/pep8/blob/master/pep8.py#L67

It'd probably be cool for setoptconf to abstract away the home directory expansion, but I haven't looked too hard into this idea.