Support underscore in command name

[evis]

Fixes #304.

[ex0ns]

Thanks for the PR, shouldn't it be |\p{N}|_]+) instead of |\p{N}_]+) (note the additional |). I have tested and both seems to work but I would prefer the version with the | if you don't mind.

Also, maybe we should add it the the second part of the regex in the command method as I think that telegram's username can contains _ as well

Edit: I was wrong about the regex, sorry for that, we should in fact remove the vertical bar | from the group otherwise we will accept commands with it, it does not serve as an OR inside a bracket. If you don't have time to do it in this PR I will open another one after.

Thanks for the fix