Is your feature request related to a problem? Please describe.
Generating text/images/svg can slow down rendering a lot.

Describe the solution you'd like
Allow to cache things either during serve (memory), or across multiple builds (filesystem).
A cache option could be added. If boolean value, use hash of the code block's contents as ID.
Otherwise use cache option value as ID. Only useful for cross-builds cache.
Items can then be deleted from the cache by deleting the files in /tmp with the ID as name.