JSZip version 3

[Landeers]

Hi,
I had problem with jszip 2.x on Angular6 so I've made an update of jszip version, all functions that use this library are now asynchronous. I let you checkout the result if you want to merge it.
Best regards

[edi9999]

I think it is not a good idea to move to the async version of JSzip, since docxtemplater and zipping are CPU intensive tasks, using Promises will hurt performance and users can already run the generation in the background using workers or webworkers.

See #340 (comment)

[bertho-zero]

Why stay obsolete? I can not generate large docs and since JSzip v3 there have been a lot of fixes.

Why do we have to do synchronous? even if we can use workers, it should be a choice and not an obligation.

[edi9999]

JSZip v3 never got any commits since Nov 2017, so it is not that much more frequently updated.

JSZip v3 is asynchronous only.

If we update to JSZip v3, that will mean that much of the docxtemplater code will also need to be asynchronous (also in modules), and it would not be possible to run docxtemplater synchronously anymore.

If we need to make a choice between full sync or full async, I prefer full sync because it will be more performant as this is a CPU intensive task.

If there is an other zip library that works well synchronously and is maitained, I would be inclined to migrate to that.