Changed double hyphens in TCW20 to em-dashes

[bleekere]

This PR addresses #16

[trishaoconnor]

These changes look good to me. Merging this to dev as they are straight-forward updates.

[trishaoconnor]

Thank you for spotting this. Great work in bringing the TCWs in line with the Guidelines.

[bansp]

Just wondering, with a view to future practice: if the original was:

space+hyphen+hyphen+space

isn't it more natural, and perhaps closer to the author's intention, for the result to be

space+ndash+space

rather than

mdash

?

[ebeshero]

We have been following a general rule that applies the en dash in ranges, as in 0–9, and the longer em dash for emphatic/dramatic separation to make an idea stand out, as in this particular edit. Here’s an explanation: https://www.grammarly.com/blog/punctuation-capitalization/dash/

I did find some discussion of an alternate approach preferred by some British English writers to set the en dash with spaces around it as you suggest. But we are following this other way to make our style consistent when we are providing guidance and information. After some discussion, though, we are not always following the em dash rule in the Guidelines examples if we are representing a different usage in a source document.

[bansp]

Thanks for the explanation, I was hoping that both styles were on an equal footing. Oh well, I'll try to bear that sad rule in mind ;-)