Various optimizations and cosmetics

Update AUTHORS file with Gabriel and me
update XCHG macro to work correctly in if statements
Add new lookup tables for block_idx and fdec/fenc addresses
Slightly faster array_non_zero_count_mmx (patch by holger)
Eliminate branch in analyse_intra
Unroll loops in and clean up chroma encode
Convert some for loops to do/while loops for speed improvement
Do explicit write-combining on --me tesa mvsad_t struct
Shrink --me esa zero[] array
Speed up bime by reducing size of visited[][][] array