GH-14: escape single quotes at beginning of lines

See the "CONTROL CHARACTERS" section in the groff(7) manual for details.

Thanks to Nick Fagerlund <github.com/nfagerlund> for reporting this bug.
inhibit periods at line beginnings with \& escape
escape text line backslashes as "\e" per groff(7)
better documentation for escaping in normal_text()
it's better to escape backslashes as \[rs] than \e

See "Single-Character Escapes" section in groff(7).
Merge branch 'issue-14' into patch