Match vpic-api behavior

[sshane]

Or have it match this library's behavior, so it is more of a drop-in replacement. I thought a formal issue would be a good idea to track this and for discussion.

• For example, invalid or foreign (format, check digit, and/or model year character bad) VINs throw an immediate exception instead of returning an object where you can check an error code/text field. I think it is best if you can parse as much of the VIN that VPIC lets you (even if just make), with some error field

• Standardize return values: does None for electrification_level mean unknown or no electrification?

  In [11]: TypedClient().decode_vin('5FNRL6H4X').electrification_level
  Out[11]: ''

• Partial decoding would be nice, but not required

  In [16]: TypedClient().decode_vin('4T1C31AK').electrification_level
  Out[16]: 'HEV (Hybrid Electric Vehicle) - Level Unknown'
  
  In [17]: VIN('4T1C31AK').electrification_level
  ValueError: VIN must be exactly 17 characters long

• Model year is an int in this library, and a string in vpic-api