Added new USB_DeviceState variable to keep track of the current Device mode USB state.
Added new Endpoint_ClearStatusStage() convenience function to assist with the status stages of control transfers. Removed vague USB_IsConnected global - test USB_DeviceState or USB_HostState explicitly to gain previous functionality. Removed USB_IsSuspended global - test USB_DeviceState against DEVICE_STATE_Suspended instead. Fixed possible enumeration errors from spinloops which may fail to exit if the USB connection is severed before the exit condition becomes true.