First sigil/standalone scripts POC

[Lucassifoni]

WIP on Sigils.
Currently not able to use the multi-letter sigil syntax in the repo since .tool-versions wants elixir 1.12. I'm only showing it as a call to sigil_NODE/2.

~NODE"""
...
"""

Nice-to-haves

• interpolation syntax in the sigil
• function call strategy : define an inline script in a way it becomes an anonymous function with arity N, arguments being passed as stdin ?
• user-configurable formatting (I'm showing my sample with Prettier here but it must be pluggable)

[Lucassifoni]

I think formatting will also always fail under Elixir 1.15