add user commands to allow for remapping

[mbpowers]

This exposes the rest of the private commands as user commands to allow for user remapping. I didn't test all the commands but I tried to set the correct nargs and pass <q-args> when necessary. Not sure if this is the ideal way to expose them but it was enough to get it working.

[luk400]

Hi, thanks for the contribution. I'm not sure why it's necessary to add these as commands though, you should just be able to remap each of them directly, no?

[mbpowers]

Ah yep! Not sure at this point, but I remember having trouble with remapping the functions, but it works fine now. I'm used to plugins exposing commands so that might've thrown me for a loop but the example in the readme is quite clear, but its been a while so I'm not sure.

That aside, I think these could still be useful for anyone opting not to use keybinds, as it reduces the amount of typing necessary to call a function. I only use keybinds myself though.