Creating a init package to load the default backend for the user platform.

[andrebq]

The old way to import the backend is to include 3 files in every project that uses go.wde one for each platform.

With this patch the user can simply import "github.com/skelterjohn/go.wde/init" and the right backend will be compiled.

If the user want to load a different backend he instead will load manually each backend (falling back to the old behaviour)

[skelterjohn]

ty