major step forward

+ split openTAWS into multiple crates in a workspace
  + `aviation_database` contains data of airports
  + `taws_minimal` is a `no_std` reference implementations of a taws
  + `kd_tree` implementation of nearest neighbour lookup
  + `kd_tree_sort` implementation of kd tree generator
  + `opentaws` core library containing alert functionalities
+ add aviation_database interface and implementation
+ add kd_tree implementation for nearest neighbour lookup in aviation
  database
+ start implementation of PDA, Mode3 and Five Hundred Foot Altitude
  Callout
+ started investigating a new test case generator strategy

.gitignore

@@ -11,3 +11,5 @@ target
 report/
 **/result
 **/result-doc
+
+aviation_database/airports.json