Improve config file and multi-developer support

Resolves issue #5.

Instead of just storing the haxelib folder path in .haxelib I changed it to a json config file. It now stores server info as well as a username, after submitting your first package. This will allow anyone in the contributors list to submit a package to the haxelib server.

Note: You will need to setup haxelib again because your config file will be invalid on the first run.