Add configurable error callback

[joernlenoch]

Replace console.error with a configurable option. This mimcs the current
default behaviour to guaranteee compatibility with previous versions.
Add errorCallback to the README.md

[khanbot]

Hey @j-lenoch,

Thanks for the PR! Mind signing our Contributor License Agreement?

When you've done so, go ahead and comment [clabot:check] and I'll check again.

Yours truly,
khanbot

[khanbot]

Hey @j-lenoch,

Thanks for the PR! Mind signing our Contributor License Agreement?

When you've done so, go ahead and comment [clabot:check] and I'll check again.

Yours truly,
khanbot

[joernlenoch]

[clabot:check]

[khanbot]

Hey @j-lenoch,

Thanks for the PR! Mind signing our Contributor License Agreement?

When you've done so, go ahead and comment [clabot:check] and I'll check again.

Yours truly,
khanbot

[edemaine]

This looks like a nice feature to add, but we should first merge #656 which provides a general framework for defining options; then we can add an errorCallback to the options object.

[edemaine]

@j-lenoch #656 finally landed. (Sorry for the delay.) Can you try to merge your feature addition onto the current master branch, e.g. via git rebase and resolving the conflict?

[joernlenoch]

Thank you very much, I'll take care of it!

[kevinbarabash]

LGTM. Sorry for the delay.

[kevinbarabash]

@j-lenoch thanks for the PR.