Allow pillow upgrade to latest (#2757)

This PR removes the sphinx `seqdiag` support as is broken with recent versions of pillow. There is only one affected diagram in the documentation so this has been replaced with a `.png` image.

The restriction on `pillow` version has been removed to satisfy #2755.

Sequence diagrams are only used here https://smingdev.readthedocs.io/en/latest/information/tasks.html.

docs/requirements.txt

@@ -6,7 +6,6 @@ m2r2==0.3.3.post2
 breathe==4.35.0
 sphinxcontrib-wavedrom
 sphinx-copybutton
-sphinxcontrib-seqdiag
 jinja2>=3.0.3
 setuptools>=57.5.0
-pillow==9.5.0 # V10 breaks seqdiag
+pillow

docs/source/conf.py

@@ -48,7 +48,6 @@
 extensions = [
     'm2r2',
     'breathe',
-    'sphinxcontrib.seqdiag',
     'link-roles',
     'sphinxcontrib.wavedrom',
     'sphinx_copybutton',

docs/source/information/tasks.rst

@@ -17,31 +17,7 @@ The BasicTask class
 This class uses the task queue plus a timer to provide an easy way to write a background task.
 All you need to is define a *loop()* function which does the work. The task has three states:
 
-.. seqdiag::
-   :caption: Task states
-   :align: center
-
-   seqdiag task-states {
-      activation = none;
-      node_width = 80;
-      node_height = 60;
-      edge_length = 160;
-      span_height = 5;
-      default_shape = roundedbox;
-      default_fontsize = 12; 
-
-      SUSPENDED [label = "suspended"];
-      RUNNING [label = "running"];
-      SLEEPING [label = "sleeping"];
-
-      SUSPENDED -> RUNNING [label = "resume()"];
-      SUSPENDED -> SLEEPING [label = "sleep()"];
-      RUNNING -> SLEEPING [label = "sleep()"];
-      RUNNING -> SUSPENDED [label = "suspend()"];
-      SLEEPING -> RUNNING [label = "resume()"];
-      SLEEPING -> RUNNING [label = "timer expired"];
-      SLEEPING -> SUSPENDED [label = "suspend()"];
-   }
+.. image:: tasks.png
 
 To see this in operation, have a look at the :sample:`Basic_Tasks` sample.