Convert the project to use the GNU Build System (aka Autotools)

LICENSE was renamed COPYING because otherwise `autoreconf` complains loudly.
This is also the reason AUTHORS, INSTALL, and README were created.

Man pages were moved into src/pam_panic/man and src/pam_panic_pw/man.

Finally, certain variables are passed through the config.h file to the
module rather than as -D flags on the command-line.

src/pam_panic/pam_panic_password.h

@@ -5,6 +5,8 @@ DATE :         2018-03-27T02:34:08+02:00
 LICENSE :      GNU-GPLv3
 */
 
+#include "config.h"
+
 #ifndef PPASSFILE
   #error PPASSFILE must be declared!
 #endif