Promisify tests and packager function

[malept]

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:

Converts all tests to use Promises (and gets rid of the waterfall dependency), and adds Promise support to the packager function via pify.

This is technically a breaking change, because the return value of packager has changed.

Fixes #627.

[MarshallOfSound]

For the record these are massive changes and I've reviewed to the best of my understanding of the changes, when GitHub doesn't show you the diff of a JS file because it is too big you know you've got a large PR 😆

The logic conversion seems sound and I don't think any nitpicks I might have over code style should block this PR being merged especially when linting seems OK with everything 👍

[Jmclerck]

I assume from looking at the release notes for the most recent versions of electron-packager this change hasn't been released yet? If not the Docs are a little confusing as it suggests that the Promisified versions of the API should already work when in fact they don't.

Is there an ETA on a release containing these changes?

Thanks!

[malept]

All of the docs are based on the current state of master. If you want the docs for the released version, you'll need to look at the docs for a given version's tag.

I have about 3 more breaking changes to do before I release, and I do all of this work in my spare time, so I don't have an ETA, sorry.

[Jmclerck]

Hi @malept thanks for the clarification and quick reply. No problem about the ETA, I just wanted to check in case you had any idea.

Thanks for all your work on this, it is appreciated!