Support for Ruby

[alexanderadam]

This is basically a followup from 421

[LouisStAmour]

https://sorbet.org/ I've been waiting for this a LOooNg time :)

That said, it has rough edges: https://dev.to/aaronc81/first-impressions-of-sorbet-a-ruby-type-checker-3ef7

Some form of types will be part of Ruby 3: https://twitter.com/darkdimius/status/1119115657776209920

Ruby bindings for the mostly C++ sorbet SDK are at https://github.com/AaronC81/sorbet-cfg

Sorbet itself is documented at https://github.com/sorbet/sorbet/blob/master/docs/internals.md