Enable JSZip compression

[pimlottc-gov]

We are using pptxgenjs to generate a fairly large deck (250+ slides) and our file size is starting to reach the limits of the mail server. I was surprised to notice that the pptx as output does not use any compression.

Currently, our workaround is to manually open and resave the file from Powerpoint, which uses compression. But it would great to have pptxgenjs do this for us. JSZip does support the "deflate" compression algorithm.

If there might be performance concerns, this could be done as an optional setting; either a flag in pptgenjs like enableCompression: true or an jszipOptions argument that is passed on to JSZip.

[gitbrent]

The main export methods need to be updated to take options objects instead of method/export name to allow for a boolean 'compress' option, so i'm pushing to v3.5.0

branch 'zip-compression' created.

JSZip API: compression

[gitbrent]

Thanks for the suggestion @pimlottc-gov

This is complete and will be in v.3.5.0 (Pull #883)

pptx.writeFile({ fileName: 'CompressDemo', compresion: true });