Parsing:  Simplified dash and ellipsis.

This originated with @dubiousjim's observation in #1419
that there was a typo in the definition of enDash.
It returned an em dash character instead of an en dash.

I thought about why this had not been noticed before, and
realized that en dashes were just being parsed as regular
symbols.

That made me realize that, now that we no longer have
dedicate EnDash, EmDash, and Ellipses inline elements, as
we used to in pandoc, we no longer need to parse the
unicode characters specially.  This allowed a considerable
simplification of the code.

Partially resolves #1419.