cli: `glide command`

[tmandry]

Add a cli subcommand to execute any glide command. This will give flexibility to people who want a more customized keybind setup than we support currently.

The hardest part is probably naming it.

[tmandry]

The challenge is parsing the commands. Right now we define commands as enums and use serde, but it's not obvious how to wire them into Clap (or vice versa, define commands using Clap and decode them from toml).