Use standalone distro per @SheetJSDev suggestion

[gabrieljoelc]

This is per @SheetJSDev suggestion:

The distribution has standalone single-file versions such as https://github.com/SheetJS/js-xlsx/blob/master/dist/xlsx.core.min.js

I guess you need to be good with the jszip requirement not being obvious and that this uses a minified file.

[SheetJSDev]

@gabrieljoelc FWIW i plan on replacing the jszip library with something more robust (combined with https://github.com/SheetJS/js-cfb to support password-protected files), so it's probably better this way. I can add the non-minified file if that's preferable

[gabrieljoelc]

Sounds good. Minified doesn't bother me. I'll let @such decide. :)