bump to OSRM 4.4 release
update links in README.md
pick up latest round of changes to fix link order
yet another git sha bump to OSRM 4.4 release
Pull the corresponding osrm-backend revision by release tag:

- Update environment variable to resemble https://github.com/mapnik/mapnik-packaging/pull/184
Merge pull request #74 from Project-OSRM/prepare_4.4_release

prepare 4.4 release