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.

@@           Coverage Diff           @@
##           master     #248   +/-   ##
=======================================
  Coverage   56.85%   56.85%           
=======================================
  Files          27       27           
  Lines        4406     4406           
=======================================
  Hits         2505     2505           
  Misses       1657     1657           
  Partials      244      244

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0088976...6115b1d. Read the comment docs.

[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.

[vitorarins]

Well I am a newbie in specification of languages. But this Ohm seems very visual, which I am very fond of it.