swr: rewrite resample_common/linear_float_sse/avx in yasm.

Linear interpolation goes from 63 (llvm) or 58 (gcc) to 48 (yasm)
cycles/sample on 64bit, or from 66 (llvm/gcc) to 52 (yasm) cycles/
sample on 32bit. Bon-linear goes from 43 (llvm) or 38 (gcc) to
32 (yasm) cycles/sample on 64bit, or from 46 (llvm) or 44 (gcc) to
38 (yasm) cycles/sample on 32bit (all testing on OSX 10.9.2, llvm
5.1 and gcc 4.8/9).
measure
swr: convert resample_common/linear_int16_mmx2/sse2 to yasm.

Speed not yet tested, mmx2/32bit not yet tested, win64 not yet tested.