lib/parseman: recognize all troff space escapes

parsetext() recognizes escapes for \& zero-width space, and \| narrow space (1/6 em-space in troff). Recognize also \^ - half-narrow space (1/12 em) and ignore it (found e.g. in dd(1)), and \0 - digit-width space and map it to plain space character (found e.g. in text(9)).

dd(1) still has some instances of \^ leaked into the output but that’s because not all .XY macros apply parsetext consistently.

Recompiled .dis file is not included in the PR.

PS: Sorry, I’m not sure why this PR shows two commits, including my last merge, though the diff itself is sane. In my repo the branch only has one commit. Might be easier to apply this trivial patch manually it Bitbucket insists on polluting the history.