Refactor the arlunio-image directive to be based on the figure directive

[alcarney]

• The .. arlunio-image:: directive now defers to the behaviour of the standard .. figure:: directive. This should make it compatible with any builder that supports .. figure::
• It now works by preprocessing the user's source code to produce an image file on disk before passing that reference onto the figure directive.
• It supports all figure options as well as 2 additional arlunio-image specific options
  • :include-code: Flag to indicate whether the source code should be included.
  • :gallery: <name> Option to specify if an image should be included in the gallery called <name> (Currently not used)

This should go some way towards resolving #236

[codecov]

Codecov Report

Merging #237 into develop will decrease coverage by 4.61%.
The diff coverage is 52.66%.

@@             Coverage Diff             @@
##           develop     #237      +/-   ##
===========================================
- Coverage    64.26%   59.65%   -4.62%     
===========================================
  Files           25       23       -2     
  Lines         1321     1113     -208     
===========================================
- Hits           849      664     -185     
+ Misses         472      449      -23     

Flag	Coverage Δ
#unittests	59.65% <52.66%> (-4.62%)	⬇️

Impacted Files	Coverage Δ
arlunio/tk/__init__.py	34.21% <ø> (ø)
arlunio/tk/components.py	41.66% <ø> (ø)
arlunio/raytrace/render.py	15.12% <15.12%> (ø)
arlunio/raytrace/camera.py	27.77% <27.77%> (ø)
arlunio/raytrace/object.py	29.41% <29.41%> (ø)
arlunio/shape.py	32.81% <32.81%> (ø)
arlunio/pattern.py	38.09% <38.09%> (ø)
arlunio/raytrace/material.py	40.62% <40.62%> (ø)
arlunio/color.py	50.00% <50.00%> (ø)
arlunio/raytrace/data.py	53.65% <53.65%> (ø)
... and 29 more

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