Initial vehicle API support

This pull request adds a vehicle/ subdirectory which adds initial support for a vehicle api based on the w3c automotive business group draft: https://rawgit.com/w3c/automotive-bg/master/vehicle_spec.html

So far only vehicleSpeed is suported and only the "get()" operation.

Related to (but doesn't completely fix) XWALK-865
Yes, you misunderstand what I meant. line 197 should be 4-space, line 198 and 199 should be 4-space plus 2-space(align the para). 

The basic guideline 2-space, 4-space or align para is:
* For unfinished line, 4-space at least, if align para like more nice as above code, please align.
* For finished line, 2-space indent.