Merge: compiler: Added prefix and suffix support for `Char`

As discussed in #1734, here's the PR for the support of prefixed characters.

For now only u and b are supported, respectively to get the code point as an int and the ascii code as a byte.

Pull-Request: #1991
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --cc src/modelize/modelize_property.nit
Simple merge