Docker compatibility: makefile and headers (#17)

* Docker compatibility: makefile and headers
- _GNU_SOURCE required for F_SETSIG
* Remove duplicate makeright.sh script
* Update some includes that don't exist on modern Linux (termio.h); Clang in Docker
  has trouble resolving them automatically

src/timer.c

@@ -46,11 +46,7 @@ unsigned long tick_count = 0; /* approx 18 ticks per sec            */
 #include <stdio.h>
 #include <signal.h>
 #include <unistd.h>
-#ifdef LINUX
-#include <linux/fcntl.h>
-#else
 #include <fcntl.h>
-#endif
 
 #ifdef ISC
 #include <sys/bsdtypes.h>

src/unixcomm.c

@@ -37,7 +37,10 @@ Unix Interface Communications
 #elif APOLLO
 #include </sys5/usr/include/termios.h>
 #elif LINUX
-#include <termio.h>
+#include <termios.h>
+/* this was called termio in the past, but no longer
+ * see https://man7.org/linux/man-pages/man7/termio.7.html
+ */
 #elif MACOSX
 #include <termios.h>
 #elif FREEBSD