Calculate hits on each filter

[crossan007]

Part of #10

When run with -h, calculate the number of hits each filter matches on the mailbox.

Produces results like:

[[Filter]]
Query = "from:([email protected])"
Archive = true
Read = false
Delete = false
ToMe = false
ArchiveUnlessToMe = false
Label = "P2/Pluralsight"
ForwardTo = ""
Hits = 5

[crossan007]

This depends on #12, which I just discovered has some issues.