Fixed bug causing overcalculation of character HP.

This was very much an edge case, as it would only occur when a character
set a number of class levels, had their HP calculated, and then set
their class levels to a lower value.
Enabled lookup of feats with specializations.

This means that Skill Focus and Weapon Proficiencies may now be looked
up, along with others I don't know about.

However, the current implementation assumes that there are no feats with
parentheses in the name. As of this commit, there are none of which I am
aware.