Sixteen bit hash for strings

[zherczeg]

Binary size unchanged. 12% improvement on bitops-nsieve-bits.js

Benchmark	Perf (sec)
3d-cube.js	1.148 -> 1.139 : +0.793%
3d-raytrace.js	1.261 -> 1.253 : +0.644%
access-binary-trees.js	0.645 -> 0.638 : +0.968%
access-fannkuch.js	2.803 -> 2.840 : -1.335%
access-nbody.js	1.315 -> 1.312 : +0.232%
bitops-3bit-bits-in-byte.js	0.633 -> 0.624 : +1.443%
bitops-bits-in-byte.js	0.931 -> 0.919 : +1.365%
bitops-bitwise-and.js	1.504 -> 1.493 : +0.708%
bitops-nsieve-bits.js	2.222 -> 1.953 : +12.117%
controlflow-recursive.js	0.460 -> 0.457 : +0.479%
crypto-aes.js	1.237 -> 1.227 : +0.801%
crypto-md5.js	0.803 -> 0.787 : +2.001%
crypto-sha1.js	0.759 -> 0.750 : +1.108%
date-format-tofte.js	0.924 -> 0.920 : +0.366%
date-format-xparb.js	0.513 -> 0.507 : +1.198%
math-cordic.js	1.617 -> 1.605 : +0.733%
math-partial-sums.js	0.877 -> 0.876 : +0.183%
math-spectral-norm.js	0.668 -> 0.669 : -0.083%
string-base64.js	2.157 -> 2.160 : -0.127%
string-fasta.js	2.018 -> 2.018 : +0.031%
Geometric mean:	+1.218%

[LaszloLango]

LGTM

[dbatyai]

LGTM