clean up stdio_impl.h
this header evolved to facilitate the extremely lazy practice of
omitting explicit includes of the necessary headers in individual
stdio source files; not only was this sloppy, but it also increased
build time.
now, stdio_impl.h is only including the headers it needs for its own
use; any further headers needed by source files are included directly
where needed.
diff --git a/src/stdio/__string_read.c b/src/stdio/__string_read.c
index de002fc..7b50a7e 100644
--- a/src/stdio/__string_read.c
+++ b/src/stdio/__string_read.c
@@ -1,4 +1,5 @@
#include "stdio_impl.h"
+#include <string.h>
size_t __string_read(FILE *f, unsigned char *buf, size_t len)
{