As others have mentioned:

* $$2^n$$ for latex, renders fine on all browsers

* ![]() for images

* []() for links, including cross-links

    ** The link syntax is [<text to link>](<link path>), so for example [this is a link](http://google.com)

    ** Markdown ## Headers have an anchor with their name (e.g. `#Headers`), so you can cross-reference any other 
    section of any other note in the git repo by just using [see this section](./path/to/other/note.md#that-section)

I have a simple CI service on my git repo that checks for broken links, so that if I move a file I get a CI error if there are broken links to it.