some documentation

[Langlaeufer]

Fixes # .

• set priority of highway=track to 2.0 to get the tracktype if present.

Changes proposed in this pull request:

• add some documentation
• remove junction roundabout (this should normally never come to evaluation)

@pgRouting/admins

[cvvergara]

I am not a cyclist What I can say is that priorities is a subjective number and at the end it will depend on the application requirements. that been said I don't mind changing a value on priority. About the junction, I don't know, I added that line so long ago and I am not a cyclist. So maybe you can find a junction and put an image in a comment on how it looks with and without the junctions.

[Langlaeufer]

Priority is used for the order of evaluating the values of the mapconfig. If it has a second meaning in the routing function this may lead to logical conflicts. In this special case: If we let priority of highway=track at 1.0 then the tracktype lines with lower priority (1.1-1.5) will be never be evaluated because highway=track and tracktype=* should normally be attached to a way at the same time.

[cayetanobv]

Thanks @Langlaeufer