Reflect Raku rename

[sumanstats]

As the language is renamed to Raku and this is the most complete package that supports Raku, it is better to inherit that here.

This PR is to reflect that and I have made following changes:

• change scope name of grammars file
• rename of grammars file
• rename spec file
• add filetypes rakumod rakutest rakudoc
• arrange filetypes based on priority, old extensions will be deprecated anyway
• change name from Perl 6 --> Raku in raku.cson
• change description in package.json to The Raku Programming Language Highlighter
• edit contributing.md, change extensions of escape and unescape files
• rename lp6iym.p6 to lriym.raku

[hankache]

Shouldn't we move this package to the Raku org?

[JJ]

@hankache we probably should.

[lizmat]

I understand Naoum Hankache lived close enough to the Beirut blast to have family members in hospital. I suspect Naoum has different things on his mind now.