Exponent Strategy

I've been playing around with exponent strategies in Alsophila and came up with what I think is a decent way of selecting them. It is also the first Alsophila feature I have ported back to Aften. The expstr_fast (-fba) option is now expstr_search (-exps) and ranges from 1 to 32.

The previous way of doing this was to select from 5 preset exponent strategy sets for each channel in a frame. The pre-defined sets were originally chosen pretty much by guessing. The new way selects from the 32 sets in the E-AC-3 specification (table E2.14). I sorted them in order of the most commonly used sets by testing various source material and analyzing which sets were used. The new search size option determines how far down this sorted list the encoder searches in order to find the best match.