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.
Move the constant term computation from
InterlinkNetworks::estimate_distance() into the new function
MultilaterationAlgorithm::make_constant_term(). This will avoid
duplicate this code into the future FBCM::estimate_distance().
Matteo Cypriani