I have a library installed at:
C:\HaxeToolkit\haxe\lib\zame-miscutils

and figured that I had to add it in the khafile.js ??
project.addLibrary('zame-miscutils');

Which seem to add it in the korefile.js ?!

	project.addSubProject(Solution.createProject('C:/HaxeToolkit/haxe/lib/zame-miscutils/git'));
}

and the files are installed in:
C:\HaxeToolkit\haxe\lib\zame-miscutils\git\org\zamedev\lib

and I write:

import org.zamedev.lib.UrlLoaderExt;

I get this error:
Type not found : org.zamedev.lib.UrlLoaderExt

EDIT: Is there a khafile.js manual ?

In Kha you only take care of khafile, korefile is generated automatically for native targets. Khafile manual can be found here:
https://github.com/KTXSoftware/Kha/wiki/khafile.js

Not sure why your library is not working though, you can probably track the difference with some library that works, or provide a test project.