Move towards API

[beckyjackson]

Resolves #78

This is a first pass. I made sure that all the "operations" accepted actual arguments, rather than the command line args. I also added some errors that a command line user would probably never see, but somebody using the API may see.

@jamesaoverton - would you like even more separation between the CLI and the API?

[jamesaoverton]

Yes, this is what I was asking for. Thanks!

One important change: library functions (i.e. functions designed to be called from other code) should not call sys.exit, they should raise exceptions. I only saw one of these in the diff, but there could be more.

It's also better not to print from library functions. You moved a bunch of prints to the run functions, which is the better approach. I still see a few prints in the library functions. If it's easy to get rid of them, that would be best.

I would have put all the run functions in cli.py, but I guess it doesn't make a big difference.

[jamesaoverton]

This is good, but I'd like one more change: I'd like to be able to get at all the main commands with a single import cogs then cogs.add. I think the best way to do that is in cogs/__init__.py with from cogs.add import add for each main command.

I think this change will cause some problems with the imports cogs/cli.py, mainly with the msg() calls. Maybe they could be moved into cogs/cli.py.

[jamesaoverton]

Great!