Add overmap special json

	new file:   overmap_specials.json
Selecting/verifying overmap special placement locations
First test (crashes)
Successful test run
Update flags/connections/placement code
Round out Json entries

Still missing crater, river, house.

Crater and river both require blob implementation, never seen random house spawn in game, so not sure what to do with it.
Testable version of new system with old specials
Added rotation.  Still needs cleanup and json review
Dynamic spawns + BLOB pattern
Change how flags work, classic mode support
Remove references to old specials
Merge remote-tracking branch 'dda/pr/7537' into dda-master

* dda/pr/7537:
  Remove references to old specials
  Change how flags work, classic mode support
  Dynamic spawns + BLOB pattern
  Added rotation.  Still needs cleanup and json review
  Testable version of new system with old specials
  Round out Json entries
  Update flags/connections/placement code
  Successful test run
  First test (crashes)
  Selecting/verifying overmap special placement locations
  Add overmap special json
Restyle overmap.cpp and give overmap_specials.json a tab-ectomy.
Remove redundant distance calculation method and call the one from line.cpp.