Rework copyright notices

While at it, rename mystrtonum.[ch] to strtonum.[ch].

Makefile

@@ -1,6 +1,6 @@
 # otpcli - command-line interface for HOTP and TOTP
 #
-# Written in 2020 by Lucas
+# Written in 2020-2021 by Lucas
 #
 # To the extent possible under law, the author(s) have dedicated all
 # copyright and related and neighboring rights to this software to the
@@ -17,18 +17,16 @@
 P =	otpcli
 V =	0.0
 
-HDR =		err.h mystrtonum.h otp.h
-OBJ =		cli.o err.o mystrtonum.o otp.o
-SRC =		${OBJ:.o=.c}
-DIST_FILES =	COPYING Makefile ${HDR} ${SRC}
+HDR =	err.h strtonum.h otp.h
+OBJ =	cli.o ${HDR:.h=.o}
+SRC =	${OBJ:.o=.c}
+
+LIBS =	-lcrypto
+
+DIST =	COPYING Makefile ${HDR} ${SRC}
 
 all: otpcli
 
-${OBJ}: ${HDR}
-
-otpcli: ${OBJ}
-	${CC} ${LDFLAGS} -o $@ ${OBJ} -lcrypto
-
 clean:
 	rm -f otpcli ${OBJ} ${P}-${V}.tgz
 
@@ -36,12 +34,16 @@ test: all run-tests.sh
 	sh ./run-tests.sh
 
 dist: clean
-	pax -w -s '#^#${P}-${V}/#' ${DIST_FILES} | gzip >${P}-${V}.tgz
+	pax -w -s ',^,$P-$V/,' ${DIST} | gzip >$P-$V.tgz
 
 install: all
 	mkdir -p ${PREFIX}/bin
 	cp -f ${BIN} ${PREFIX}/bin
-	cd ${PREFIX}/bin && chmod 555 ${BIN}
 
 uninstall:
 	cd ${PREFIX}/bin && rm -f ${BIN}
+
+${OBJ}: ${HDR}
+
+otpcli: ${OBJ}
+	${CC} ${LDFLAGS} -o $@ ${OBJ} ${LIBS}