replace set_avoided_tags with avoid_tag & add 'cost' argument

doc/en/scripting/builtins/libpathfinding.md

@@ -55,6 +55,12 @@ pathfinding.pull_route(agent: int) --> table<vec3> or nil
 --- Set the maximum number of visited blocks for the agent. Used to limit the amount of work of the pathfinding algorithm.
 pathfinding.set_max_visited(agent: int, max_visited: int)
 
---- Set a list of tags defining avoided blocks
-pathfinding.set_avoided_tags(agent: int, tags: table<string>)
+--- Adding an avoided blocks tag
+pathfinding.avoid_tag(
+    agent: int,
+    -- tag for avoided blocks
+    tag: string, [optional],
+    -- cost of crossing a block
+    cost: int = 10
+)
 ```