getAnglePairs returns pairs of azimuth angles. For every pair of two neighbouring winDoors
the two angles will point at the two azimuthy winDoor edges closest to the neighbour
winDoor.
The angles are constrained to the interval [0; 2*Math.PI]. This limit will have to
be fixed if one wants to make houses that span wider than this interval, such as
spiral houses.
fixed #53 and #83
Fixed a few small bugs