Convert OpenType Feature File specification to Markdown

[miguelsousa]

Continuation of #776

[miguelsousa]

@frankrolf I'm done with my changes and also implemented Read's suggestions.

Unless you have further tweaks, I think the only remaining item is the TOC.

[frankrolf]

@miguelsousa Thank you for this. I think changing the TOC to match the system proposed in the document structure might not be possible – I tried it earlier.
As of this moment, the TOC is just a system of nested, numbered lists like this:

1. item one
2. item two
   1. item two_one
   2. item two_two
      1. item two_two_one
      2. item two_two_two
      3. item two_two_three
   3. item two_three
3. item three

The GitHub markdown parser decides to put lowercase Roman numerals first, then alphabetic indexing – opposite to the way the spec works at the moment. The source code for the TOC is purely numerical:

1. item one
2. item two
    1. item two_one
    2. item two_two
        1. item two_two_one
        2. item two_two_two
        2. item two_two_three
    3. item two_three
3. item three

I tried to match that code to what’s set up in the document itself, but it breaks the whole system.
I am glad to update the numbering structure within the document to match whatever GitHub is proposing, but I think it may be different in another markdown interpretation.

[miguelsousa]

Thanks, I'll look into it. I'd like to try some stuff.