Add tests to ci

Test pyflix and simulation using pytest.
Fix running the sim in non-tty environment.
Test presence of some essential files in the docs.

gazebo/Arduino.h

@@ -134,8 +134,9 @@ public:
 
 	int available() {
 		// to implement for Windows, see https://stackoverflow.com/a/71992965/6850197
+		if (!isatty(STDIN_FILENO)) return 0;
 		struct pollfd pfd = { .fd = STDIN_FILENO, .events = POLLIN };
-		return poll(&pfd, 1, 0) > 0;
+		return poll(&pfd, 1, 0) > 0 && (pfd.revents & POLLIN);
 	}
 
 	int read() {