Add BPMN support

[nekator]

add support to render BPMN diagram via bpmn-js
GH-44

[ggrossetie]

Thank you very much @nekator
It looks great! 👍

I will do a more in depth review this week.

[nekator]

You are welcome. Looking forward for your feedback. 😀

[ggrossetie]

Sorry I didn't have time to give it a try yet but since it's a new container we will need to update the following pages:

• https://github.com/yuzutech/kroki/blob/master/docs/modules/setup/pages/install.adoc#images
• https://github.com/yuzutech/kroki/blob/master/docs/modules/ROOT/pages/architecture.adoc

[nekator]

I'll take a look into the docs and update the relevant parts today or tomorrow.

[nekator]

I updated the docs for install and architecture. I also changed the caching version to the diagram version.

[ggrossetie]

Overall it's looking very good, thanks @nekator
I left a few comments but I can take care of them if you want.

I wonder if we should remove the XML header from the SVG. Currently, bpmn-js will generate the following SVG:

<?xml version="1.0" encoding="utf-8"?>
<!-- created with bpmn-js / http://bpmn.io -->
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="856" height="587" viewBox="150 75 856 587" version="1.1">
<!-- ... -->

Maybe it can be configured...

[nekator]

I will and the relevant changes tomorrow.

Regarding XML header i would suggest to keep it.

Maybe we should make it configurable to support other output formats because bpmn-js supports multiple formats.

[nekator]

Resolved everything and squashed it to a single feature commit.

[ggrossetie]

Regarding XML header i would suggest to keep it.

I don't have a strong opinion, so we will keep it for now.

Maybe we should make it configurable to support other output formats because bpmn-js supports multiple formats.

Oh nice, I didn't know!
@nekator I guess that since they are using a <canvas> we can export it to png using toDataURL. Is that what you had in mind?
But as far as I understand, it's only possible to save as SVG using the Viewer API (ie. BaseViewer.prototype.saveSVG) right?

I think we can add additional output formats in follow-up pull requests. Wdyt?

[ggrossetie]

Code is looking really good. Well done @nekator 👍

[nekator]

Adding additional formats would be another PR IMO. For now it is good to have BPMN diagram to svg. I will take a look into other formats maybe this weekend.

I'm glad you like the code and that you took the time to review it properly. Thank you 😊