Add ways for people to create their own custom listeners without using regex

[Xetera]

We don't want to deal with catastrophic backtracking stuff so this would just be a premium feature for searching user input. A (--i) flag could be added to make the matching case insensitive.

This should take priority over cleverbot responses
Command layout:
$listen { listened command } [ --options ] | { response }

Example:
$listen anime sucks --i | No u