Ambiguitity resolution changes. (1) RESOLVE AMBIG-AMBIG will now correctly add a count to say G if R (AG) and S (CG) are being compared; if there are multiple overlap (e.g. B (CGT) and D(AGT)), then 1/overlap will be added to each (e.g. 0.5 to G and 0.5 to T). (2) The -ambig option now takes a list of characters that will be resolved; e.g. -a RY will resolve R and Y but average all other ambigs