Parser improvements.

[zherczeg]

The number of delete opcodes is reduced to two from six. The range of numbers which can be included in the byte code is doubled from (-127,127) to (-256,256).

Slight (1%) improvement, but 3% on access-fannkuch.js.

Benchmark	Perf (sec)
3d-cube.js	1.271 -> 1.257 : +1.094%
3d-raytrace.js	1.511 -> 1.498 : +0.859%
access-binary-trees.js	0.739 -> 0.732 : +0.947%
access-fannkuch.js	3.050 -> 2.949 : +3.313%
access-nbody.js	1.512 -> 1.505 : +0.466%
bitops-3bit-bits-in-byte.js	0.690 -> 0.669 : +2.983%
bitops-bits-in-byte.js	1.004 -> 0.985 : +1.934%
bitops-bitwise-and.js	1.904 -> 1.989 : -4.482%
bitops-nsieve-bits.js	2.424 -> 2.346 : +3.245%
controlflow-recursive.js	0.526 -> 0.507 : +3.556%
crypto-aes.js	1.403 -> 1.360 : +3.029%
crypto-md5.js	0.886 -> 0.872 : +1.583%
crypto-sha1.js	0.834 -> 0.820 : +1.712%
date-format-tofte.js	1.129 -> 1.133 : -0.348%
date-format-xparb.js	0.576 -> 0.587 : -1.839%
math-cordic.js	1.794 -> 1.771 : +1.280%
math-partial-sums.js	1.044 -> 1.033 : +1.141%
math-spectral-norm.js	0.760 -> 0.757 : +0.372%
string-base64.js	4.643 -> 4.631 : +0.246%
string-fasta.js	2.196 -> 2.191 : +0.218%
Geometric mean:	+1.083%

Binary size unchanged.

[LaszloLango]

LGTM

[dbatyai]

LGTM