Pre-run condition checks on commands

[eritbh]

Allow commands to set permissions that are required to execute the command. This could be done by a list of flags or a function which returns true or false based on the message that contains the command.

[eritbh]

Alternatively, just pass commands a permissions dict of true/false values and let the command figure its own stuff out. Doesn't opinionate the logic but still eliminates the need of each command to manually calculate permissions.

[eritbh]

Or just allow permission.has or whatever... though having a way to integrate more tightly with the help command would be nice. I've been thinking about this a lot and still don't know how best to handle it.

[eritbh]

I'll actually just implement this as a function you pass that does this. The function will be able to return a boolean or a promise for one, and that boolean will determine whether or not the command is executed.

[eritbh]

Because screw everything I already said about it. If it were gonna be a function you might as well just include it in the main function process; providing an object of options makes more sense to me. Further thoughts will be in #12.

[eritbh]

fixed with #12