Be more aggresive classifying Roundabout Intersections.

Roundabout Intersections are roundabouts with up to four ways and turn
angles which makes the turns obvious, e.g. as in:

```
    *
    *
* *   * *
    *
    *
```

but not

```
     *
    *
* *   *
    * *
     * *
```

For Roundabout Intersections we issue instructions such as
"turn <direction>" instead of "take the <nth> exit".

At the moment we have a limit on the radius for these Roundabout
Intersections of 5 meters. Which fails to classify a wide range of
Roundabout Intersections in the US (with the US-wide streets).

This changeset removes the Roundabout Intersection radius limit:

- if the roundabout is larger than a threshold and is named we classify
  it as a rotary

- if the roundabout matches our criteria for Roundabout Intersections
  we classify it as a Roundabout Intersection

- else fallback to plain old Roundabout

There is a second issue with determining a roundabout's radius.
But that's for another pull request (tracking in #2716).

References:
- https://github.com/Project-OSRM/osrm-backend/issues/2716

features/testbot/side_bias.feature

@@ -53,10 +53,10 @@ Feature: Testbot - side bias
             | bcegb  | roundabout |
 
        When I route I should get
-           | waypoints | route    | turns                           |
-           | a,d       | ab,cd,cd | depart,roundabout-exit-1,arrive |
-           | a,f       | ab,ef,ef | depart,roundabout-exit-2,arrive |
-           | a,h       | ab,gh,gh | depart,roundabout-exit-3,arrive |
+           | waypoints | route    | turns                                         |
+           | a,d       | ab,cd,cd | depart,roundabout turn left exit-1,arrive     |
+           | a,f       | ab,ef,ef | depart,roundabout turn straight exit-2,arrive |
+           | a,h       | ab,gh,gh | depart,roundabout turn right exit-3,arrive    |
 
      Scenario: Mixed Entry and Exit
         Given the profile "lhs"