font-weight issue

Hey there,
Using **svg2png**, I can not generate PNG with correct font-weight.
For instance I want to use the black version of my font (which is well installed). (font-weight = 900)
It seems font-weight attribute is **limited to few values**, is this normal ?

How can I generate a PNG using the right font-weight value ?

Here is an example, I have 2 different SGV but the generated PNG are the same

SVG1: `Hello World`
SVG2: `Hello World`

Start by reproducing the issue through the svg2png entry point with the two SVG snippets using font-weight 700 and 900. Trace how CairoSVG handles font-weight during SVG text rendering; done means installed fonts render visibly different weights when the SVG requests distinct values.

Written by the indexing model from the issue text.