v2 - sans syntax error

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Bloody typical, you wait around for ages hoping for a new routing
capability to be added to mkgmap and then two come along on
the same day.

I've been trying to discover how unpavedness is encoded for at least 6
months. Every now and again, I return to think about it some more.
Check and re-check the same old data structures. Very
frustrating, no progress. Damn those cunning bastards at Garmin....

However, a month or two ago, I discovered that Table C contains more
than just turn restrictions. I still don't know many of it's little
secrets but, today, having exhausted all other possibilities, I finally
twigged that Table C contains the key to understanding "unpavedness".
Gotcha!

The attached patch allows you to add either unpaved=yes/true/1 or
paved=no/false/0 to a way and then it will be ignored for routing
purposes when the GPS has been told to avoid unpaved roads.

Not sure if those are the best tags to use - any thoughts?

BTW - the unpaved road line type 0x0a has nothing to do with
unpavedness, it's just a routable way that gets drawn as a dashed line
(default rendering).

Feedback, etc.

Mark