Merge: Native Types

Since we plan on conforming with UTF-8, chars can no longer be of C char type, this PR changes the internal representation of a Char to become capable of holding an arbitrary Unicode code point.

Since chars become unsigned entities, and since NativeString will hold Byte values soon, its c type has been changed to unsigned char* as preparation for the migration

This is all related and necessary for #1262.

Pull-Request: #1407
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>
Reviewed-by: Jean Privat <jean@pryen.org>