Remove hard dependency on readline, split makefile config into config.mk

Makefile

@@ -1,9 +1,6 @@
 PREFIX = /usr/local
 
-CC       = cc
-CFLAGS   = -std=c99 -pedantic -fpic -O2 -Wall -Wextra -Wno-override-init -I. -Ilua-5.4
-CPPFLAGS = -D_DEFAULT_SOURCE -DLUA_USE_READLINE
-LDFLAGS = -lm -lreadline
+include config.mk
 
 OBJS = csto.o lcallisto.o lcl.o lenviron.o lextra.o lfile.o \
 	   ljson.o lprocess.o lsocket.o util.o

config.mk

@@ -0,0 +1,8 @@
+CC       = cc
+CFLAGS   = -std=c99 -pedantic -fpic -O2 -Wall -Wextra -Wno-override-init -I. -Ilua-5.4
+CPPFLAGS = -D_DEFAULT_SOURCE
+LDFLAGS = -lm
+
+# Enable readline
+#CPPFLAGS += -DLUA_USE_READLINE
+#LDFLAGS  += -lreadline

shell.nix

@@ -3,7 +3,6 @@ pkgs.mkShell {
 	nativeBuildInputs = with pkgs.buildPackages; [
 		bmake
 		clang
-		readline
 	];
 	shellHook = "alias make=bmake";
 }