Unify coding style

@sjaeckel integrated clang-format with formal coding style. Run his
script and commit changes.

There are pros and cons of this commit.

Mixed coding style is a "broken window". A good single style simplifies
reading and writing code.

On the other hand, this is a big change which will lead to conflicts.

src/rand.h

@@ -16,8 +16,8 @@
 #ifndef __LIBSTROPHE_RAND_H__
 #define __LIBSTROPHE_RAND_H__
 
-#include <stddef.h>     /* size_t */
-#include "strophe.h"    /* xmpp_ctx_t */
+#include <stddef.h>  /* size_t */
+#include "strophe.h" /* xmpp_ctx_t */
 
 typedef struct _xmpp_rand_t xmpp_rand_t;