Add CLI config parsing

[jpsim]

It'd be useful to override .liftoffrc config options with command line arguments. i.e. liftoff --use_cocoapods=false.

I have a branch in progress that I'll push up soon with a possible implementation.

I know the whole point of .liftoffrc was to avoid passing in cli arguments, but sometimes I want to create a quick project with a different setting than what I have in .liftoffrc.

Thoughts @thoughtbot/ios?

[gfontenot]

Weird that didn't ping @thoughtbot/ios.

I'm all for this. I've been thinking about this the past few days anyway. At the very least, we should have a way to bypass the initial prompt by passing --name, --company, --identifier and --prefix options at launch.

[gfontenot]

This was completed in 080b30d and c6a05f8