Add mermaid support

**Is your feature request related to a problem? Please describe.**
Graphviz requires system dependencies. This could prevent users getting a good experience with Burr.

**Describe the solution you'd like**
[Mermaid](https://pypi.org/project/python-mermaid/) diagrams I believe require less to get working.

[Jupyter support](https://blog.jupyter.org/jupyterlab-4-1-and-notebook-7-1-are-here-20bfc3c10217).

Thing to figure out:
- you still need something to render the mermaid markdown programmatically if someone wants to create a png.
- github can natively render the mermaid markdown -> so png might not be required (for this initial implementation).
- I believe npm has a CLI that would be installed to work here - and would require someone to install it for things to work..

**Describe alternatives you've considered**
N/A

**Additional context**
Feedback from a user.