feat(combat): support self targeted and area skills

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

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

More player like behavior.

fix(combat): dispose cancellation token in use skill

fix(combat): make skill cancellation tokens actions async

feat(combat): add combat operations