Add mermaid support

[skrawcz]

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 diagrams I believe require less to get working.

Jupyter support.

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.

[zilto]

Other notes:

• Mermaid in a markdown block (```mermaid) will render on GitHub, but not in other markdown engine (e.g., requires a VSCode extension)
• AFAIK, there's no way to render Mermaid from Python. You need to have access to Javascript, which seems like a more burdensome dependency (random example found on Medium)
• While Graphviz has Python bindings, Mermaid doesn't and would require manually handling strings (see Haystack's code)
• From my experience (with Haystack at least), rendering Mermaid is significantly slower than rendering graphviz in a notebook

(IMHO, this might not be a good first issue. It is well-scoped, but expect significant amount of work to complete the task)