[Variable Fonts] font naming/metadata proposal

We've been working on two beta VF fonts MarkaziText #1565 and Vollkorn #1571. I thinks it's important we get the metadata for variable fonts established before we sign off on these.

Myself and @davelab6 have been discussing naming in #1571. The STAT table also adds another layer of complexity.

Atm I'm using fontmake's default naming. For Markazi Text #1565 we get the following nametable:

```
platformID encodingID languageID nameID nameString
1 0 0 256 Weight
1 0 0 257 Regular
1 0 0 258 Medium
1 0 0 259 SemiBold
1 0 0 260 Bold
3 1 1033 0 Copyright 2017 The Markazi Text Authors (https://github.com/BornaIz/markazitext)
3 1 1033 1 Markazi Text
3 1 1033 2 Regular
3 1 1033 3 1.000;NONE;MarkaziText-Regular
3 1 1033 4 Markazi Text Regular
3 1 1033 5 Version 1.000
3 1 1033 6 MarkaziText-Regular
3 1 1033 8 Borna Izadpanah and Florian Runge
3 1 1033 9 Borna Izadpanah (Arabic designer), Fiona Ross (Arabic design director) and Florian Runge (Latin designer)
3 1 1033 11 http://www.borna.design, http://www.florianrunge.com
3 1 1033 12 http://www.borna.design, http://www.florianrunge.com
3 1 1033 13 This Font Software is licensed under the SIL Open Font License, Version 1.1. This license is available with a FAQ at: http://scripts.sil.org/OFL
3 1 1033 14 http://scripts.sil.org/OFL
3 1 1033 256 Weight
3 1 1033 257 Regular
3 1 1033 258 Medium
3 1 1033 259 SemiBold
3 1 1033 260 Bold
```

I've manually created the following STAT table
```

```

This gives us the following font menus in Desktop applications


Finally, for filenames we will distinguish between Roman and Italic VF fonts. When Markazi moves out of Beta its filename will be:

`MarkaziText-Roman-VF.ttf`

*Note: 'Roman' and 'VF' will not be added to the names inside the fonts.*

When a family includes Italics as a separate VF font, the filenames will be the following:

`Vollkorn-Roman-VF.ttf`
`Vollkorn-Italic-VF.ttf`

We want to end up with the following font menu.


When we're happy with this proposal, our next step is to write a Font Bakery test.