Convenience tokens for reading / construction. about bitstring HOT 2 CLOSED

It might be preferable to instead steal from Python's struct module:

b -> int:8
B -> uint:8
? -> uint:1
h -> int:16
H -> uint:16
l -> int:32
L -> uint:32
q -> int:64
Q -> uint:64

4*B -> uint:8, uint:8, uint:8, uint:8

An idea is to use the byte order character at the start as an indicator that 
this is
a 'struct-like' format string. Then we won't need the commas!

@ -> native byte ordering
> -> big endian
< -> little endian

>>> pack('>hhl', 1, 2, 3)

Done in revision 454. Will be available in version 0.5.2.