More log options

[s0lst1ce]

Describe the command you'd like
Bot owners should have more power over the control of the log from discord. Because of this it would be nice to add stop and clear subcommands to log. This is especially useful after a bug report when you don't want the log file to be growing.
Additional adding the possibility to change the log level (ex: DEBUG -> INFO) could be useful.

What needs to be done:

• Implement stop command
• Implement start command
• Implement clear command
• Implement level command
• Write documentation for commands