Add Support for Custom Themes in mkdocs-exporter

[nihalshah-dev]

Hi folks,

Many thanks for this wonderful plugin. I have some quick suggestion for improvements -

Description
Currently, mkdocs-exporter has hardcoded support for only the material and readthedocs themes. This limitation prevents users from using forked or custom themes without modifying the plugin source code manually.

Use Case
Many users customize the Material for MkDocs theme or create entirely new themes to better fit their documentation needs. However, since mkdocs-exporter directly imports only predefined themes, any custom theme results in errors or unexpected behavior like below -
RuntimeError: The theme you are using (my-docs-theme) is currently not supported by MkDocs Exporter, sorry.

Proposed Solution
Introduce custom theme support by allowing users to specify their theme in mkdocs.yml, similar to how MkDocs itself allows custom themes.

Example Proposal in mkdocs.yml

plugins:
  - exporter:
      theme: my_custom_theme

Instead of hardcoding the theme imports, modify the exporter to dynamically detect and load themes. This would allow any custom theme to be used without modifying the plugin itself.

Let me know if it makes any sense!! Thanks✌

[nbanyan]

From what I can tell, that error refers to whether there are scripts for making adjustments to a page based on chosen MkDocs theme. It probably wouldn't be hard to have it use an empty 'theme' if something other than Material or RTD is used.

Does setting the exporter theme to material or readthedocs cause any errors or rendering issues with your theme?