Use something other than font-kit and/or put it behind feature gate

[fu5ha]

font-kit seems like a nice lib, however it's very much not pure Rust, requiring not only a full c++ build system but also several C libs and their associated header files to be installed on a system (at least on Linux), and as such presents a fairly significant bar to entry. It would be nice not to depend on it. Also, even after getting it to compile on Fedora, I stlil get this output in my terminal when runing the todos example, though it does seem to work at least.

edit

error output was fixed by updating outdated fontconfig-devel.

Just for reference, on Fedora 30, I had to install cmake, g++, freetype, freetype-devel, expat-devel, and fontconfig-devel for it to work.

[hecrj]

This seems to be caused by libfontconfig, which compiles and statically links itself if it can't find an appropriate system version with pkg-config. Here is the relevant code: https://github.com/servo/libfontconfig/blob/master/build.rs#L20

That said, a feature gate would be nice for cases where system font loading isn't needed (for instance, when embedding fonts in games).

[AlienKevin]

Just in case someone on ubuntu wants to install these missing dependencies:

sudo apt install pkg-config
sudo apt install cmake
sudo apt install libfreetype6-dev
sudo apt-get install expat
sudo apt-get install libexpat-dev

After installing the above, the counter example builds successfully.

[valpackett]

servo/libfontconfig#55 would add a force_system_lib feature to libfontconfig that would allow us to get an error instead of building the silly/annoying cache-incompatible embedded fontconfig