Feature overview matrix for Raku compilers

This is an attempt to collect an overview of implemented features in
contemporary Raku compilers.
It powers the web page http://raku.org/compilers/features .

The idea is to have a concise and easy-to-write source file which contains the
data, and a script that converts this information into a format that is easy
to read, like a colored HTML table or so.

A first version of that script is process.pl, which needs perl 5.10 or
newer and HTML::Template::Compiled from CPAN. It writes the xhtml output
to standard output, or to the filename specified on the command line.

A feature should appear in the table if any of the following applies:
 * it is very useful to the end user
 * it is a distinguished Raku feature (e.g. grammars, junctions)
 * it is hard to implement
 * it showcases differences between compilers
 * its implementation drives spec development

The "forgiveness > permission" principle applies, and the authors are
very forgiving.

Your contribution is very welcome. Please join our discussions in #raku,
http://raku.org/community/irc

A cron job automatically updates the web page at
http://raku.org/compilers/features from this repository. It runs at least
once per hour.