WIP: Add formal specification of the language

[i4ki]

This PR introduces the formal specification of the language. What do you guys think? Is it better than EBNF? The link to ohm editor with nash's gramar is here: https://ohmlang.github.io/editor/#fca725147857c09bb442be1ce03048e0

Yes, there's some js to validate the grammar until ohm has a Go parser. Still thinking the best way to install ohm-js dependency and run the grammar check from 'make test'. Maybe ran with docker?

[codecov-io]

Codecov Report

Merging #248 into master will not change coverage. The diff coverage is n/a.

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  Misses       1657     1657           
  Partials      244      244

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[ryukinix]

Really interesting thing! I miss a lot checkers of EBNF grammar, I search a lot and didn't find anything really good; mostly just legacy, dead or just too painful too use. This ohm is a quite nice. I'm still think that ebnf is nice to read as human being, but have all that software of ohm doing the parsing, show-case of AST and other stuff is really great!

Seems pretty fine to me running the ohm tests inside of docker through make test. Formal tests it's important.