extract optimized parser from binary string into separate module

[romsahel]

See this PR for details: DockYard#204

Except this time I moved the refactor/optimization into its own module since the original repo does not seem to want to merge this change.
With this module side-by-side with the original, we can remain in sync and benefit from fixes made to the parser and renderer.

Here is a benchmark of this version:

##### With input large #####
Name                       ips        average  deviation         median         99th %
RFC2822Binary             2.56      390.00 ms     ±1.36%      389.94 ms      399.54 ms
RFC2822 (legacy)          1.42      704.02 ms     ±8.70%      682.41 ms      811.63 ms

Comparison:
RFC2822Binary             2.56
RFC2822 (legacy)          1.42 - 1.81x slower +314.01 ms

Memory usage statistics:

Name                     average  deviation         median         99th %
RFC2822Binary          547.98 MB     ±0.00%      547.98 MB      547.98 MB
RFC2822 (legacy)       290.44 MB     ±0.00%      290.44 MB      290.44 MB

Comparison:
RFC2822Binary          547.98 MB
RFC2822 (legacy)       290.44 MB - 0.53x memory usage -257.54533 MB

Seeing some more benchmark, I think there is still room for improvement though - especially with some of the string operations. From the fprof profile (on a 1.84M-line test email):

Regex.replace/4            41 calls   1925ms total
String.replace/3           15 calls   1924ms total
Regex.apply_list/5     384408 calls   1154ms own time
:re.loopexec/8         192248 calls    769ms own time