Fix missing documentation for many clock faces:

* Move from .c to .h as needed for consistency.
* When missing from both, copy from pull request or wiki.
* When missing entirely, infer functionality from source code.

movement/watch_faces/complication/interval_face.h

@@ -22,16 +22,62 @@
  * SOFTWARE.
  */
 
-//-----------------------------------------------------------------------------
-
 #ifndef INTERVAL_FACE_H_
 #define INTERVAL_FACE_H_
 
-#include "movement.h"
-
 /*
-A face for customizable interval timers
-*/
+ * INTERVAL TIMER face
+ *
+ * This face brings 9 customizable interval timers to the sensor watch,
+ * to be used as hiit training device and/or for time management techniques.
+ *
+ * - There are 9 interval timer slots, you can cycle through these with the
+ *   alarm button (short press). For each timer slot, a short "slideshow"
+ *   displaying the relevant details (like length of each phase - see below)
+ *   is shown.
+ *
+ * - To start an interval timer, press and hold the alarm button.
+ *
+ * - To pause a running timer, press the alarm button (short press).
+ *
+ * - To completely abort a running timer, press and hold the alarm button.
+ *
+ * - Press and hold the light button to enter settings mode for each interval
+ *   timer slot.
+ *
+ * - Each interval timer has 1 to 4 phases of customizable length like so:
+ *   (1) prepare/warum up --> (2) work --> (3) break --> (4) cool down.
+ *   When setting up or running a timer, each of these phases is displayed by
+ *   the letters "PR" (prepare), "WO" (work), "BR" (break), "CD" (cool down).
+ *
+ * - Each of these phases is optional, you can set the corresponding
+ *   minutes and seconds to zero. But at least one phase needs to be set, if
+ *   you want to use the timer.
+ *
+ * - You can define the number of rounds either only for the work
+ *   phase and/or for the combination of work + break phase. Let's say you
+ *   want an interval timer that counts 3 rounds of 30 seconds work, 
+ *   followed by 20 seconds rest:
+ *         work 30s --> work 30s --> work 30s --> break 20s
+ *   You can do this by setting 30s for the "WO"rk phase and setting a 3
+ *   in the lower right hand corner of the work page. The "LAP" indicator
+ *   lights up at this position, to explain that we are setting laps here.
+ *   After that, set the "BR"eak phase to 20s and leave the rest as it is.
+ *
+ * - If you want to set up a certain number of "full rounds", consisting
+ *   of work phase(s) plus breaks, you can do so at the "BR"eak page. The
+ *   number in the lower right hand corner determines the number of full
+ *   rounds to be counted. A "-" means, that there is no limit and the 
+ *   timer keeps alternating between work and break phases.
+ *
+ * - This watch face comes with several pre-defined interval timers,
+ *   suitable for hiit training (timer slots 1 to 4) as well as doing
+ *   work according to the pomodoro principle (timer slots 5 to 6).
+ *   Feel free to adjust the timer slots to your own needs (or completely 
+ *   wipe them ;-)
+ */
+
+#include "movement.h"
 
 #define INTERVAL_TIMERS 9     // no of available customizable timers (be aware: only 4 bits reserved for this value in struct below)