The commit message in 1a2b47463b45c2b05ec80ade28781afc986576af is incorrect -- the package seemed to work because only the help message was invoked: result/bin/txt2man -h To guard against such trivial successes, this commit introduces a test.
Tested on Mac OS X 10.10, Nix 1.11.4 with: nix-build -A txt2man result/txt2man
txt2man converts flat ASCII text to man page format. (Solfege, which is added in the next commit, needs this.)
