string-buffer: New module.

* lib/string-buffer.h: New file.
* lib/string-buffer.c: New file.
* modules/string-buffer: New file.
* doc/posix-functions/open_memstream.texi: Mention the new module.

modules/string-buffer

@@ -0,0 +1,26 @@
+Description:
+A buffer that accumulates a string by piecewise concatenation.
+
+Files:
+lib/string-buffer.h
+lib/string-buffer.c
+
+Depends-on:
+stdbool
+attribute
+stdarg
+vsnprintf-posix
+
+configure.ac:
+
+Makefile.am:
+lib_SOURCES += string-buffer.c
+
+Include:
+"string-buffer.h"
+
+License:
+LGPLv2+
+
+Maintainer:
+all