Libraries: Create top level directory for libraries.

Things were getting a little crowded in the project root, so this patch
moves the Lib*/ directories into Libraries/.

Libraries/LibC/sys/uio.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+__BEGIN_DECLS
+
+struct iovec {
+    void* iov_base;
+    size_t iov_len;
+};
+
+ssize_t writev(int fd, const struct iovec*, int iov_count);
+
+__END_DECLS