adding the code to py_pwm.c to get the error data out of c_pwm.c. general code cleanup. this should close #56 as the softpwm code had the error string support already in it

source/py_gpio.c

@@ -127,7 +127,6 @@ static PyObject *py_setup_channel(PyObject *self, PyObject *args, PyObject *kwar
       init_module();
    }
 
-
    if (direction != INPUT && direction != OUTPUT)
    {
       PyErr_SetString(PyExc_ValueError, "An invalid direction was passed to setup()");