Suggestion: Links and a little sugar on compiler matrix

[Su-Shee]

• Add links to the appropriate githubs/websites of Rakudo, Rakudo/Nom and Niecza within the feature matrix on http://perl6.org/compilers/features
• Add which compiler is based/written in/needs what language
• Add a date so people can see how recent the feature matrix actually is
• Link feature x to synopsis x (or appropriate) so people can look up easily what a certain feature means

[coke]

links are done. date is added.

[moritz]

Everything except the second suggestion is now implemented. I don't want to add a more verbose description of the compilers, people can just follow the links.

Thanks for your suggestions!