Support Python 3k

This is attempt to support Python 3k in biggles (see #42). Note that the branch is **not ready to be merged**. Although the code in this branch compiles, it still segfaults at runtime. The purpose of this pull request is to make the code review easier.
OK. So this works. Man this was a pain to figure out. Can @esheldon confirm I did the reference counting correctly? I don't want to cause a memory leak.

	tmp1 = PyObject_CallMethod(key,"encode",NULL);
                skey = PyBytes_AsString(tmp1);

		tmp2 = PyObject_CallMethod(value,"encode",NULL);
                svalue = PyBytes_AsString(tmp2);
		
		pl_setplparam( params, skey, svalue );

                Py_XDECREF(tmp1);
                Py_XDECREF(tmp2);