Improved clear command

[s0lst1ce]

My feature request is about

• Changing a feature

Describe the solution you'd like
The clear command (see #7 ) would benefit from gaining these options:

• clearing all messages from a defined period of time (instead of a number of message)
• clear messages from a specific user. Either in the channel or globally. This could also be mixed with a time feature

Describe alternatives you've considered
For global clearing another command could be used as a measure of security.

Additional context
This could be easily implemented with the purge coroutine of dpy.

What needs to be done

• Add a time selection
• Add a user selection
• Add a global setting to delete messages from the entire server
• Update documentation

[s0lst1ce]

Won't add the global selector since this is kinda overpowered for the clear command and would require some tinkering which would further impact performance.