Added a tiny implementation of readline library, based on linenoise sources.

See https://github.com/antirez/linenoise for details.

Implemented a routine atexit() in libc.

Pdc modified to use readline library.

lib/Makefile

@@ -1,5 +1,5 @@
 TOPSRC          = $(shell cd ..; pwd)
-SUBDIR		= startup libc libcurses libtermlib libwiznet
+SUBDIR		= startup libc libcurses libtermlib libwiznet libreadline
 PROG		= ar as aout ld nm ranlib size strip
 
 CFLAGS          += -std=gnu89 -fno-builtin -g -Werror -Wall -DCROSS -I. \

lib/libreadline/Makefile

@@ -0,0 +1,17 @@
+TOPSRC		= $(shell cd ../..; pwd)
+include $(TOPSRC)/target.mk
+
+vpath %.c $(TOPSRC)/src/libreadline
+
+CFLAGS		+= -B$(TOPSRC)/lib/ $(DEFS) -Wa,-x -Wall -Werror
+
+OBJS		= readline.o
+
+all:            ../libreadline.a
+
+../libreadline.a: ../ar ../ranlib $(OBJS)
+		../ar rc $@ $(OBJS)
+		../ranlib $@
+
+clean:
+		rm -f *~ *.o a.out *.a