Don't add spaces to punctuation; replace -- with em dashes

[Herschel]

The original plugin manually handled text wrapping, and spaces were spliced in after ellipses and dashes to make the wrapping work better. This isn't necessary now that GDI is handling the wrapping, as it seems to wrap at the punctuation correctly. Removing this can avoid an unsightly extra space after dashes-- like this.

gdifonts can render the full range of Unicode, so also replace double hyphens -- with an em dash — for aesthetics.

[onimitch]

Looks good. Thanks for noticing the tests file needs to be saved in ShiftJIS. I'll merge this and your other PR and test them for a bit before putting out a new release