use program_options in osrm-prepare

Use boost program_options in osrm-prepare.

The usage is changed a little bit: you can pass just the .osrm input file, and ".restrictions" will automatically be appended to get the path the to restrictions file. Or you can use the --restrictions switch to manually specify the path to the restrictions file.

As with osrm-extract, you can use a config file  but it's not included in the repo. It looks for 'contractor.ini' by default, or you can specify the path with the --config switch. And you can use --threads to set number of threads, and --profile to specify the lua profile.