hgrc.5: fix quoting of literal strings The quotes would go wrong in many places due to differences between asciidoc version 8.2.7 used by Benoit and 8.4.5 used by me. Between those versions asciidoc stopped interpreting the content of `quoted strings`, and so `*` would start bold text in the old version, but do nothing in the new version. To complicate things further, `\*` would escape the bold tag in the old version, but in the new version the backslash was inserted literally into the output (because the backtick quotes it). I've now replaced backticks with non-quoting plusses and escaped backslashes as appropriate.