Currently OSRM parses traffic signal nodes without consideration
for the direction in which the signal applies. This can lead
to duplicated routing penalties, especially when a forward and backward
signal are in close proximity on a way.
This commit adds support for directed signals to the extraction and
graph creation. Signal penalties are only applied in the direction
specified by the OSM tag.
We add the assignment of traffic directions to the lua scripts,
maintaining backwards compatibility with the existing boolean
traffic states.
As part of the changes to the internal structures used for tracking
traffic signals during extraction, we stop serialising/deserialising
signals to the `.osrm` file. The traffic signals are only used by
`osrm-extract` so whilst this is a data format change, it will not
break any existing user processes.
