Remove --target (again) in favor of specifying --install-lib

This is a follow-up to https://github.com/numenta/nupic/pull/197

As it turns out, if you specify --target, pip assumes you're installing a pure-python lib, and makes some assumptions about where to clean up that may be wrong in some circumstances.  This PR removes the --target option in favor of --install-lib (specified via --install-option) and appears to do the right thing in our internal build environment.