Promisify apis

[oguzeroglu]

Closes #71

[oguzeroglu]

Please get rid of done entirely. This means that patterns such as this:

fromFile('test/fixtures/bpmn/error/no-xml.txt').catch(function(err) {
   expect(err).to.exist;
     done();
   });
});

...should be transformed to try { await ... } ... blocks.

In this test we benefit from the done() behavior, as we'd like to check if fromFile fails. The alternative would be:

var err;

try {
  // await stuff...
} catch(error){
  err = error;
}

expect(err).not.to.be.undefined;

Which in my opinion is not prettier, nor worth the effort just for the sake of getting rid of "done".

[nikku]

This does not only have the benefit of getting rid of done but also the benefit of being more understandable.

[oguzeroglu]

Updated the tests 👍

[nikku]

Added three changes on top:

• fix + modernize example: https://github.com/bpmn-io/bpmn-moddle/pull/73/commits/3610cd8f5eb1a937c48398cd9d3b9e60a243b907
• simplify read tests: https://github.com/bpmn-io/bpmn-moddle/pull/73/commits/0f59ee6fea1d6462e18e17317036022490f0feff

Both follow the pattern we're taking with moddle-xml.

[nikku]

Looking at the API I find it a bit odd that read returns a structured object (including warnings) while write returns the plain result (i.e. only the written XML string).

I remember we had an issue somewhere that write warnings are currently simply emitted to the console, as the current API does not support exposing it. Returning a complex object ({ xml, warnings, ... }) would allow us to export that meta-data in the future. It would also mean that we offer the same, semantic API for read and write.

Getting the XML would still be as simple as

const { xml } = await moddle.write(definitions);

What do you think?

[oguzeroglu]

I updated the API accordingly, also squashed your commits.