Feature: Support for Dependencies

[JeffersGlass]

It would be ideal to be able to allow developers to specify dependencies to be used with their code snippets.

[JeffersGlass]

This could possibly just the user writing either an html <py-config> tag into their markdown, or using a py-config custom markdown block to include one inline per block (see #3 for a related idea)

[rbarman]

@JeffersGlass, can you show an example of using the <py-config> tag? Or does this require extra changes with mkdocs-pyscript to work?