feat(combat): support self targeted and area skills

fix(combat): do not return successfully when walk position is equal to target position

Merge pull request #32 from Rutherther/combat

Add combat extension

fix(combat): wait for a second after casting a skill

This seems to be the "reload" period needed until
the character may move again

feat(pathfinding): add user cancelling to walk manager

feat(pathfinding): create custom pathfinding

fix(combat): adjust walk in range behavior to not sit idle too much

fix(combat): wait for a while after using a skill

More player like behavior.

fix(combat): dispose cancellation token in use skill

feat(combat): reset walk in range operation if the target moved

fix(combat): make skill cancellation tokens actions async

fix(combat): support minimal walk in range distance 0

feat(combat): add combat operations