All thanks to Matthias Klose, who pointed me at a workaround for the
linking issue against libcurl that I couldn't solve so far.
Now we can drop all workarounds an ugly code for downloading
screenshots, which, as a bonus, makes the whole generator much more
robust at downloading them (and causes no failures with HTTPS URLs
anymore).
https://bugs.launchpad.net/ubuntu/+source/dub/+bug/1563861
We need a sane error handling method, also, we were pulling gdk-pixbuf
via rsvg already, so using it just made sense.
Not too great in terms of dependencies, but meh...
This allows us to get rid of DYAML which was not working properly (had
test failures and did not compile on some systems).
std.json also brings some very welcome speed improvements, and we will
use it later anyway to interface with JavaScript bits in the HTML.
I based this on libGD, which seems to be both very fast, commonly used
and lightweight on dependencies.
For font rendering and probably for SVG too, we will use Cairo.
