Initial commit. Import existing work.

This is an import from the latest rejit code.
Work actually started around November 2012. The local git repository I have used
until now is to messy to push.
Updte code for fast forward SIMD paths to avoid accesses after the eos.

Other small changes:
  - Remove README to keep only the README.md file.
  - Minor changes to html resources.
  - Remove a sleep in the benchmarks script.
Add compilation help when missing libargp on MacOS.
Fix SConstruct to not build the benchmarks utils by default.
Update documentation for benchmarking utilities.
Retry fixing build on MacOs with non standard ligarp installtion.

There was an error in operators precedence.

Also includes a minor README change.
Fix tools/benchmarks/run.py
Use an absolute path for the re2 library.
Minor changes to the readme.
Refactor the flags mechanisms and add related command line options to the rejit engine.
Some cleaning up for benchmarks/run.py.
Remove code for the deprecated fast forward mechanisms.
Some cleaning.

Cleaning around regexp.h.
Update SConstruct to use lists (in some places) for the environment variables.
Some more cleaning. Also includes a fix for benchmark building.
Report re2's commit in the re2 data files instead of rejit's.
Use '#' rather than '$' to avoid matches in the benchmarks.

This is to prepare adding Google v8 to the benchmarks, which seems to do some
optimization (at least) on end of line enchors.
Update tests to test longer strings with non-matching prefix and suffix.

This helps exercising the fast forward code paths.
Remove the benchmark looking for '$'.

It is not very instructive, and I haven't managed to get coherent results for v8
on it.
Improve the code generated when multiple MCs are used for fast forward.
Add v8 to the benchmarks.

There are still a some issues with the reported performance for v8 in a few
benchmarks.