[WIP] swr: rewrite resample_common/linear_float_sse/avx in yasm.

Linear interpolation goes from 63->55 (64bit) or 66->59 (32bit)
cycles/sample, and non-linear goes from 43->41 (64bit) or 46->45
(32bit) cycles/sample in my testing, all on OSX 10.9.2 with Apple's
llvm-5.1 (XCode 5.1.1). Other people report a slowdown so this
probably needs more testing with other system/compiler combinations.
measure