* use ES6 import / export
* UTILS: export individual utilities
* TESTS: localize TestHelper includes
BREAKING CHANGE:
* all utilities export independent functions
* library sources got ported to ES6. You must now use
a ES module bundler such as Browserify + babelify or
Webpack to consume this library (or parts of it).
Async utilities properly propagate _all_ errors to the
specified _done_ callback. Failing in _done_ does not
re-invoke it.
Adjustments made in
* Viewer#importXML
* Viewer#saveSVG
* Importer#importBpmnDiagram
Tests cleaned up to remove un-necessary `if (err) { ...` snippets.
Nico Rehwaldt
Philipp Fromme
pedesen