Allow an output filename to be passed to Diagram explicitly.

[bjornt]

This allows you to have a consistent output filename, even if you decide
to tweak the diagram name.

[mingrammer]

Good job :)

Would you mind updating the documentation too? ;)

• Diagram docs page: https://diagrams.mingrammer.com/docs/guides/diagram#options
• Docs file: https://github.com/mingrammer/diagrams/blob/master/docs/guides/diagram.md

[bjornt]

Good job :)

Would you mind updating the documentation too? ;)

• Diagram docs page: https://diagrams.mingrammer.com/docs/guides/diagram#options
• Docs file: https://github.com/mingrammer/diagrams/blob/master/docs/guides/diagram.md

Sure. Done!

[jck4]

Nice! I was literally looking for this yesterday.

[mingrammer]

Thanks for your contribution :)