Merge pull request #568 from mklement0/fix_make_file

Fixed Urchin invocation problem in zsh and dash.  Makefile "future-proofed" to take advantage of true cross-shell testing with Urchin, once available.
Ensure that a system has `manpath` before invoking it.

Closes #531, fixes #557.
v0.18.0
Update `urchin`
.travis.yml now obtains latest urchin version from the npm registry instead of directly from GitHub