C arrays for `HGEdge::intermediate_points`

[yakra]

• Use a C array for HGEdge::intermediate_points instead of a list or vector.
• Include a separate intermediate_count in unused space before format. I'm thinking uint16_t, though could use uint32_t if necessary.
  • What's the largest intermediate_points.size() of any existing edge?
• Any significant speedup from using raw coords (2 doubles) instead of HGVertex*?
• Proposed here; referenced here. Carving out a new issue mostly for a good place to leave this code:

  HGEdge collapse ctor

  	// find which endpoints aren't the vertex we're collapsing and set them as our new
  	// endpoints, and at the same time, build up our list of intermediate vertices
  	auto	e1_count = edge1->intermediate_count,
  		e2_count = edge2->intermediate_count;
  	auto	new_p = intermediate_points = new HGVertex*[intermediate_count = e1_count+1+e2_count];
  
  	if (edge1->vertex1 == vertex)
  	 {	vertex1 = edge1->vertex2;
  		auto old_p = edge1->intermediate_points + e1_count;
  		while (old_p > edge1->intermediate_points) *new_p++ = *--old_p;
  	 }
  	else {	vertex1 = edge1->vertex1;
  		memcpy(new_p , edge1->intermediate_points , e1_count*sizeof(HGVertex*));
  		new_p += e1_count;
  	 }
  
  	*new_p++ = vertex;
  
  	if (edge2->vertex1 == vertex)
  	 {	vertex2 = edge2->vertex2;
  		memcpy(new_p , edge2->intermediate_points , e2_count*sizeof(HGVertex*));
  	 }
  	else {	vertex2 = edge2->vertex1;
  		auto old_p = edge2->intermediate_points + e2_count;
  		while (old_p > edge2->intermediate_points) *new_p++ = *--old_p;
  	 }

• We're down 1 line due to deleting 5 lines of debug text.
  Restoring them would make a cleaner commit diff. Do I prefer a clean diff or clean code?
  FWIW, I just now uncommented 4 of them to grep -c them.
• Consider swapping the 1st if & else for a sense of visual continuity, pattern-spotting, yadda yadda.
• std::string HGEdge::intermediate_point_string()

  {	if (!intermediate_count) return " None";
  	std::string line;
  	char fstr[56];
  	for (auto p = intermediate_points, end = p+intermediate_count; p < end; p++)
  	{	auto i = *p;
  		sprintf(fstr, "%.15g %.15g", i->lat, i->lng);
  		line += " [" + *i->unique_name + "] " + fstr;
  	}
  	return line;
  }

• Other functions affected by the change, even if calls are commented out
  • HGEdge::str()
  • Anything else?
• While I'm in there, readabilty... wall of text -> whitespace, indentation, 1 big cout with a couple ternaries.