Add missing libpng and libz for rendering bitmap glyphs

[narodnik]

Fixes #133

[bvssvni]

@narodnik Can you rebase?

[narodnik]

ok I found it easier to redo the entire commit. Plz pull it now so I don't have to do this all over again

[bvssvni]

@narodnik some of the checks are failing.

[narodnik]

The windows build works but is failing during the test because it isn't recursively checking out the submodule properly.

libz-sys contains a submodule in src/zlib to another submodule for zlib, which includes the zlib.h:

    build.include("libpng").include("libz-sys/src/zlib");

So this is an error with the CI build system, rather than the code.

[bvssvni]

Merging.

[bvssvni]

Thanks!