Add pictures for the 'allow_missing_start' of the 'check_next' procedure (see #576). Indicates in the timing diagram when the options 'allow_overlapping' and 'allow_missing_start' add no influence regarding the given example.

Author: dalex78

docs/check/images/check_next_passing.json

@@ -6,8 +6,8 @@
    {name: 'expr', wave: '0.....10'},
    {name: 'active_clock_edge', wave: '=.......', data: ['rising_edge']},
    {name: 'num_cks', wave: '=.......', data: ['4']},
-   {name: 'allow_overlapping', wave: '=.......', data: ['true']},
-   {name: 'allow_missing_start', wave: '=.......', data: ['true']}
+   {name: 'allow_overlapping', wave: '=.......', data: ['true/false']},
+   {name: 'allow_missing_start', wave: '=.......', data: ['true/false']}
  ],
  head:{
    tick:0,

docs/check/images/check_next_passing.png

@@ -0,0 +1,15 @@
+{
+  signal: [
+    {name: 'clock', wave: 'p.........'},
+    {name: 'en', wave: '1...01....'},
+    {name: 'start_event', wave: '010.......'},
+    {name: 'expr', wave: '0.....1010'},
+    {name: 'active_clock_edge', wave: '=.........', data: ['rising_edge']},
+    {name: 'num_cks', wave: '=.........', data: ['4']},
+    {name: 'allow_overlapping', wave: '=.........', data: ['true']},
+    {name: 'allow_missing_start', wave: '=.........', data: ['true']}
+  ],
+  head:{
+    tick:0,
+  }
+}

docs/check/images/check_next_passing_with_missing_start.json

@@ -7,7 +7,7 @@
    {name: 'active_clock_edge', wave: '=.........', data: ['rising_edge']},
    {name: 'num_cks', wave: '=.........', data: ['4']},
    {name: 'allow_overlapping', wave: '=.........', data: ['true']},
-   {name: 'allow_missing_start', wave: '=.........', data: ['true']}
+   {name: 'allow_missing_start', wave: '=.........', data: ['true/false']}
  ],
  head:{
    tick:0,

docs/check/images/check_next_passing_with_missing_start.png

@@ -951,7 +951,11 @@ the second start event
 When ``allow_missing_start`` is ``true`` ``check_next`` will allow
 ``expr = '1'`` when there is no corresponding start event. When
 ``allow_missing_start`` is ``false`` such a situation will lead to a
-failure.
+failure. Here is an example where ``expr`` is at ``'1'`` for one
+cycles with no corresponding start event.
+
+.. figure:: images/check_next_passing_with_missing_start.png
+   :alt:
 
 Any unknown value  (``U``, ``X``, ``Z``, ``W``, or ``-``) on ``start_event``
 will cause an error.