CLI is awkward to use

[svenstaro]

Describe the bug
I think the CLI is a bit awkward to use and overuses subcommands in favor of flags.

To Reproduce
For instance, menyoki record --root --size $(slop) apng save /tmp/hello.apng. This is somewhat awkward.

Expected behavior
How about menyoki record --size-select --format apng --output /tmp/hello.apng. I think this makes a lot more sense. We could also have a shortform -f apng -o /tmp/hello.apng.

[AlexDaniel]

Related: #43