Fix treatment of dots at start of line

[thinkerbot]

Periods at the start of a line cause issues for groff. The normal escape sequence for periods (\.) causes lines to disappear when they are the first non-whitespace characters, even though the escape works elsewhere.

One solution is to write periods at the start of a line as \[char46] (see escaping dots in groff). This commit adds this special escape and adds-to or fixes tests as appropriate.