Jeffery To authored Oct 27, 2019 and Christian Hergert committed Nov 04, 2019

This renames the "underlined" style to "net-address":

* Default styles all have logical/functional names, e.g. "constant",
  "function". The "underlined" style is the only one with a stylistic
  name.

* Almost all current uses of the "underlined" style are for URLs or
  email addresses.

The only non-address use of the "underlined" style is for
"markup-emphasis" in asciidoc.lang. This also changes this mapping to
"def:doc-comment-element" (following markdown.lang).

This also keeps the "underlined" style, mapping it to "net-address", for
backwards-compatibility with third-party language definitions.