[spelling] signalling --> signaling (#162)

Switch from the UK spelling of signalling (also, signalled and
signaller) to the American spelling.

lib/cbuf/include/lib/cbuf.h

@@ -104,7 +104,7 @@ size_t cbuf_peek(cbuf_t *cbuf, iovec_t *regions);
  * supplied data.
  * @param[in] len The maximum number of bytes to write to the cbuf.
  * @param[in] canreschedule Rescheduling policy passed through to the internal
- * event when signalling the event to indicate that there is now data in the
+ * event when signaling the event to indicate that there is now data in the
  * buffer to be read.
  *
  * @return The number of bytes which were written (or skipped).