Refactor events into their own package

Most of the existing actions are game actions (they control the player character)
so they live in actions.game. Eventually, there will be modules for different
kinds of actions that only apply to, e.g. modal UI.

erynrl/actions/action.py

@@ -0,0 +1,45 @@
+# Eryn Wells <eryn@erynwells.me>
+
+from typing import TYPE_CHECKING, Optional
+
+from ..object import Actor
+from .result import ActionResult
+
+if TYPE_CHECKING:
+    from ..engine import Engine
+
+class Action:
+    '''An action that an Entity should perform.'''
+
+    def __init__(self, actor: Optional[Actor] = None):
+        self.actor = actor
+
+    def perform(self, engine: 'Engine') -> ActionResult:
+        '''Perform this action.
+
+        Parameters
+        ----------
+        engine : Engine
+            The game engine
+
+        Returns
+        -------
+        ActionResult
+            A result object reflecting how the action was handled, and what follow-up actions, if any, are needed to
+            complete the action.
+        '''
+        raise NotImplementedError()
+
+    def failure(self) -> ActionResult:
+        '''Create an ActionResult indicating failure with no follow-up'''
+        return ActionResult(self, success=False)
+
+    def success(self) -> ActionResult:
+        '''Create an ActionResult indicating success with no follow-up'''
+        return ActionResult(self, success=True)
+
+    def __str__(self) -> str:
+        return f'{self.__class__.__name__} for {self.actor!s}'
+
+    def __repr__(self):
+        return f'{self.__class__.__name__}({self.actor!r})'