feat(editor): two free ends joined without loops or forced curves, the shape from a free end on the wheel

- the join of two free ends (a drag from one onto the other, or a click of the lay tool on it) tries in turn: a straight when the joints check can't see the kinks (half its angle), one circular arc through both ends (a piece cut out of a curve comes back as it was, its cant kept), a curve with straights where the tangents meet, a reverse curve, and only then a free Bezier curve; a curve turning more than it needs to, sharper than 10 m or longer than three chords is never taken
- the transition curves eased out of a curved neighbour only when there's room for them between the ends, never crossing each other into a loop
- cant and transition curves recommended for the radius the curve really gets, at the speed of the joined track or of the tool and never above what the radius allows; the circular arc keeps at least max(20 m, 0.4 V) between the transitions, the cant lowered to what the shortened transitions can ramp, transitions under 1 m left out
- shapes from a free end: arc then straight, straight then arc, arc through the cursor, straight; Ctrl+wheel steps the radius, Shift+wheel the shape (at a free end: the other joins), the plain wheel still zooms; a click of the lay tool from a free end lays the shape and goes on from its end
- self-test commands join, layto and joints; Polish translation

editor/editorAlignment.hpp

@@ -35,6 +35,8 @@ struct limits
 	double vertical_factor{0.4};
 	double vertical_min{2000.0};
 	double tangent_min_time{0.0};
+	double arc_min{20.0};
+	double arc_min_factor{0.4};
 };
 
 struct compound_arc
@@ -164,6 +166,8 @@ struct result
 };
 
 result compute(design const &Design);
+double speed_limit(double const Radius, limits const &Limits);
+result compute_recommended(design &Design, bool const Transitions);
 bool tangent_intersection(design const &Design, glm::dvec2 &Point);
 bool collinear(design const &Design);
 
@@ -184,4 +188,49 @@ std::size_t minimum_pieces(result const &Result, design const &Design);
 std::vector<segment_data> pieces(result const &Result, design const &Design, std::size_t const Count, std::vector<double> const &Breaks = {}, std::vector<std::size_t> const &Counts = {},
                                  std::vector<std::size_t> *Intervals = nullptr);
 
+struct join_end
+{
+	glm::dvec3 position{0.0};
+	glm::dvec2 direction{0.0, 1.0};
+	double roll{0.0};
+};
+
+enum class join_kind
+{
+	none,
+	straight,
+	arc,
+	curve,
+	reverse_curve,
+	bezier
+};
+
+struct join_request
+{
+	join_end start;
+	join_end end;
+	double radius{0.0};
+	int variant{0};
+	bool transitions{false};
+	double speed{100.0};
+	double kink{0.1};
+	transition_shape shape{transition_shape::cubic_parabola};
+	limits norms;
+};
+
+struct join_result
+{
+	join_kind kind{join_kind::none};
+	std::vector<segment_data> pieces;
+	double length{0.0};
+	double radius{0.0};
+	double cant{0.0};
+	double transition{0.0};
+	double speed{0.0};
+	int variants{0};
+	std::vector<std::string> warnings;
+};
+
+join_result join(join_request const &Request);
+
 }