Avoid brittle linking workarounds

 - Depends on https://github.com/DennisOSRM/Project-OSRM/pull/841 (travis build will fail unless/until this is merged)
 - Proper fix for #11.
 - Adds new flag to enable configuring against a `Project-OSRM` checkout in any location by doing:

```sh
# Absolute path is required due to the way gyp works
npm install --osrm=`pwd`../Project-OSRM`
```