Add more lane configurations

[1ec5]

Continuing from mapbox/mapbox-navigation-ios#576, we need more lane icons corresponding to the following common configurations:

• Left + right
• Left + through + right
• U-turn + right (which can be flipped for U-turn + left)
• Slight turns (and combinations thereof)

/cc @frederoni @danesfeder @ericrwolfe @bhousel

[1ec5]

Slight turn arrows would be useful for freeway lanes (mapbox/mapbox-navigation-ios#1267) as well as for part of the exit number display in a turn banner (mapbox/mapbox-navigation-ios#1262).

[frederoni]

Turns out we already have slight left/right.

[1ec5]

Cool, the slight right icon looks good for turn lanes. We’d probably need to lop off the bottom third if we wanted to use it for the exit number component, however. Combinations involving slight turns, such as slight right + right, are relatively rare, but they’re particularly important when they occur. I’m not sure about the best way to make all those combinations manageable.

/cc @JThramer

[1ec5]

Tangentially, I’ve also been collecting real-world examples of turn lane icons that the OpenStreetMap tagging model doesn’t support and our routing engines consequently don’t support. This Wikimedia Commons category contains all the turn lane combinations that are standard in the U.S., thanks to the more detailed standard in Ohio that elaborates on the national standard.