Show tags and categories within notebook posts

Currently tags and categories are seen when searching for a notebook (i.e. from [tag pages](https://pymc-examples.readthedocs.io/en/latest/blog/tag/pymc3model.html)), but not once the notebook is [open](https://pymc-examples.readthedocs.io/en/latest/time_series/MvGaussianRandomWalk_demo.html). Might be natively supported by [ablog](https://ablog.readthedocs.io/en/latest/)
