Pandoc filter execute

[hdinkel]

Adds filter to execute magick code.

All images are created in the '_images' directory (might need to be created first)
Existing images will not be overwritten - we might want to add a command to the makefile like clean_images

The filter will not blindly execute any codeblock, but expects a key/value pair:

generate_image [True|False]

Another switch enables the automatic generation of HTML code including the tag for the generated image:

include_image [True|False]

Example CodeBlock:

~~~{generate_image=True include_image=False}
convert -size 40x20 xc:red xc:blue -append -rotate 90 append_rotate.gif
~~~

Note: Using fenced code blocks
see http://pandoc.org/README.html#fenced-code-blocks
and jgm/pandoc#673

Current limitations:

• Image names need to be unique throughout the whole tree.
• Complex commands, such as using perl/grep/pipes etc.
• Will need to change image location for those examples which already explicitly include the image (ex. examples at the top of the antialising file)

[emcconville]

If these values will be boolean in nature, then I would argue them as flags, and can be classnames

 ~~~{.generate_image}
 //...code...
 ~~~

The the check would be as simple as..

if 'generate_image' in classes:
    # Do work