Add 2019/endoh/try.sh, helper program + formatting

The helper program ascii.c converts args passed to it to char values (if
isascii() returns non-zero) which with try.sh allows one to reconstruct
the code with the backtrace rather than having to memorise ascii(7) (and
even if they did it would be hard to put it together). One should of
course use xargs(1) and try.sh does.

The try.sh script checks that gdb is installed first, telling the user
to install it if they don't have it. The README.md file notes that for
macOS It's not a simple matter of just installing gdb - there are
additional steps.

2019/endoh/Makefile

@@ -111,7 +111,7 @@ PROG= prog
 OBJ= ${PROG}.o
 CSRC= ${PROG}.o
 DATA=
-TARGET= ${PROG}
+TARGET= ${PROG} ascii
 #
 ALT_OBJ=
 ALT_TARGET=
@@ -132,6 +132,9 @@ all: data ${TARGET}
 ${PROG}: ${PROG}.c
 	${CC} ${CFLAGS} -g $< -o $@ ${LDFLAGS}
 
+ascii: ascii.c
+	${CC} $< -o $@
+
 # alternative executable
 #
 alt: data ${ALT_TARGET}