docs/pandoc: Don't escape underscores in the middle of text

docs/pandoc: Don't escape underscores in the middle of text

Pandoc deliberately (and contrary to markdown) doesn't treat underscores in
the middle of normal text as emphasis markers, as this is almost always the
unhelpful interpretation.

For text which is emphasised using _, an underscore in the middle is
interpreted, but the emphasis marker can be switched to * instead.

One problem case is where we use {} globbing with identifier names, as it
counts as a word break.  Therefore, we do need to retain the escaped
underscore immediately following a closing brace.

No change in content - only formatting.  This results in the text being easier
to read and grep.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>