Rakuize code and documentation

[tbrowder]

• Change all references to 'perl6' to 'Raku'.
• Rename module files to '*.rakumod'.
• Rename pure pod6 files to '*.rakudok'.
• Rename all scripts with '.pl', '.pl6', or '.p6' to '.raku'.

[tbrowder]

Red is looking good. I look forward to giving it another spin!

[FCO]

This might been done with my last commits. Please reopen if I have forgotten something.