fix node engines syntax
osrm-prepare appears to no longer like restrictions as an arg
workaround #11
use npm's node-gyp to avoid needing it globally
adapt to changes (regressions?) in path handling upstream in OSRM - refs #2
adapt tests to latest develop branch at https://github.com/DennisOSRM/Project-OSRM/commit/ba12e312805969251b79d8d85db3e87114201a72