Add Functionable (Ruby Developer Experience)

[bkuhlmann]

Why

Hello. 👋 This is in response to the upcoming Ruby Developer Experience newsletter in order to share more tooling that'll enrich people's lives.

I'm the author of the Functionable gem which allows you to leverage Ruby modules as pure functional modules. This allows you to unleash the power of the functional side of Ruby which is also more performant both in terms of CPU and memory.