Performance improvement

[Marsup]

This code is consistently faster on all runs that I've made.
Worst case was :

{ http_parser: '2.6.2',
  node: '5.7.0',
  v8: '4.6.85.31',
  uv: '1.8.0',
  zlib: '1.2.8',
  ares: '1.10.1-DEV',
  icu: '56.1',
  modules: '47',
  openssl: '1.0.2f' }
Scores: (bigger is better)

alt
Raw:
 > 4.9603174603174605
 > 5.185825410544512
 > 4.344048653344918
 > 4.273504273504273
Average (mean) 4.69092394942779

jss
Raw:
 > 1.6963528413910094
 > 1.7226528854435832
 > 1.5873015873015872
 > 1.8796992481203008
Average (mean) 1.7215016405641201

Winner: alt
Compared with next highest (jss), it's:
63.3% faster
2.72 times as fast
0.44 order(s) of magnitude faster
QUITE A BIT FASTER

The test was done with bench stringifying #16's example (a smaller version of it since it took too long).

[moll]

Sorry, I haven't gotten around to this yet, @Marsup. ;)