remove Medium from font weights

[vincent-peugnet]

As it's not part of the CSS font weight properties:

https://drafts.csswg.org/css-fonts/#font-weight-prop

Same goes for extra-light, extra-bold, thin, light, semi-bold, black.

And bolder and lighter are impossible as well, as those are relative indicators only supposed to be used in the CSS attributes, not in @fontface properties.

The only authorized values for font weight is:

• bold

OR: using numbers.

What I could do from here, would be to convert extra-light to 200 et cætera, according to the given list:

• 100 - Thin
• 200 - Extra Light (Ultra Light)
• 300 - Light
• 400 - Normal // normal should not be used as it is common in style, weight and stretch.
• 500 - Medium
• 600 - Semi Bold (Demi Bold)
• 700 - Bold
• 800 - Extra Bold (Ultra Bold)
• 900 - Black (Heavy)