`hkfind`: Allow filtering on hotkey information

[Hoboneer]

Stuff like chain length and whether a hotkey permutation is within a mode would be good.

Whether a command runs upon key release or press, and whether the chord event is to be replayed for other clients would also be good. However, this would need to allow one to specify which chord in the chain is being checked.

Some potential predicates:

• -len <OPERATOR> <NAT>, -length <OPERATOR> <NAT> where OPERATOR is a relational operator (=, !=, >, etc.), and NAT is a positive integer
• -inmode [<OPERATOR> noabort_index]
• -on <EVENT> where EVENT is either press or release (it shouldn't matter which chord this is specified for, see #22)
• -replay [<OPERATOR> chord_index]

[Hoboneer]

Should index arguments allow negative values to mean that it starts from the end?