Rename c_string.{c,h} -> c_strings.{c,h}

Makefile

@@ -29,7 +29,7 @@ CFLAGS=$(CCONFIG) $(EXTRA) $(CWARN) $(G) $(O) $(OSFLAGS)
 CFLAGS_PLACEHOLDER="$$(echo -e '\033[2m<flags...>\033[m')" 
 LDLIBS=-lgc -lcord -lm -lunistring -lgmp -ldl
 BUILTIN_OBJS=builtins/siphash.o builtins/arrays.o builtins/bools.o builtins/channels.o builtins/nums.o builtins/integers.o \
-						 builtins/pointers.o builtins/memory.o builtins/text.o builtins/threads.o builtins/c_string.o builtins/tables.o \
+						 builtins/pointers.o builtins/memory.o builtins/text.o builtins/threads.o builtins/c_strings.o builtins/tables.o \
 						 builtins/types.o builtins/util.o builtins/files.o builtins/ranges.o builtins/shell.o builtins/paths.o \
 						 builtins/optionals.o builtins/patterns.o builtins/metamethods.o builtins/functiontype.o builtins/stdlib.o
 TESTS=$(patsubst %.tm,%.tm.testresult,$(wildcard test/*.tm))

builtins/tables.c

@@ -17,7 +17,7 @@
 #include <sys/param.h>
 
 #include "arrays.h"
-#include "c_string.h"
+#include "c_strings.h"
 #include "datatypes.h"
 #include "memory.h"
 #include "metamethods.h"

builtins/tomo.h

@@ -11,7 +11,7 @@
 
 #include "arrays.h"
 #include "bools.h"
-#include "c_string.h"
+#include "c_strings.h"
 #include "channels.h"
 #include "datatypes.h"
 #include "functiontype.h"