Makefile enhanced to install required test utility 'urchin' on demand, locally, via `npm install`. The urchin install test was amended to also find a locally installed version, not just a global one as before.
Makefile enhanced to error out with instructions if invoked without a target.
Changed `replace` npm package version spec. from ^ to ~.
`make list` now lists defined targets one line at a time.
'test-<shell>' targets introduced to makefile, which now defaults to running the fast, slow, and installation test suites; 'test' target now does the same for ALL shells; package.json now invokes make instead of urchin directly; make release made much more robust.
Fix to previous commit to ensure that NVM_DIR isn't unset when run by Travis.
2nd attempt to fix Travis builds.