Allow disconnections to be signaled by drivers

This allows for disconnections to be detected quickly
where possible.

It also makes sure other driver errors aren't thrown
in the event of a disconnection.

include/icsneo/communication/communication.h

@@ -37,6 +37,7 @@ public:
 	bool open();
 	bool close();
 	bool isOpen();
+	bool isDisconnected();
 	virtual void spawnThreads();
 	virtual void joinThreads();
 	bool rawWrite(const std::vector<uint8_t>& bytes) { return driver->write(bytes); }