Merge: parser: do not allocate a reduction table for each parser

This optimize multiple Parser allocation, for instance nitunit or nitdoc that need to deal with each nitunit in the documentation.

usertime for `./nitdoc ../lib/core/`:

* before: 0m2.184s
* after: 0m1.788s (-18.1%)

Pull-Request: #1770
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>