Regenerate Friis indexes at each call of the algorithm when
autocalibration is used (without this fix, FBCM given always the same
result autocalibration activated, because of the Friis indexes equal to
zero).
Add class FRBHMBasic, which derives FBCM and RADAR.
ReferencePoint: Add functions friis_index_for_ap() and
friis_indexes_for_ap() (that takes code away from
Stock::update_all_friis_indexes()).
CartographyAlgorithm and MultilaterationAlgorithm now extend
PositioningAlgorithm with "public virtual" instead of "public".
CartographyAlgorithm: select_point() must now return a ReferencePoint.
MultilaterationMethod: Add pure virtual function multilaterate_2d().
MinMax: Add function multilaterate_2d().
MultilaterationAlgorithm: Add function multilaterate_2d() to map
MultilaterationMethod::multilaterate_2d().
Makefile: Fix some dependencies.