docs: add Component examples, and include attribute docstrings.

docs/index.rst

@@ -10,15 +10,34 @@ Components
 ----------
 **esper** does not define any specific Component base class
 to inherit from. Instead, a normal Python class can be used.
-Also, while it's not required, the the `@dataclass` decorator
-from the `dataclasses` module can be useful to help write
-compact Component classes.
+Also, while it's not required, the the ``@dataclass`` decorator
+from the ``dataclasses`` module can be useful to help write
+compact Component classes. You can even use ``namedtuple``s
+for limited cases where a Component does not need to be modified.
+Some examples of valid Components::
+
+    class Velocity:
+        def __init__(self, x=0.0, y=0.0, accel=0.1, decel=0.75, maximum=3):
+            self.vector = Vec2(x, y)
+            self.accel = accel
+            self.decel = decel
+            self.maximum = maximum
+
+
+    @dataclass
+    class Camera:
+        current_x_offset:   float = 0
+        current_y_offset:   float = 0
+
+
+    Interaction = namedtuple('Interaction', 'interaction_type target_name')
 
 
 The World context
 -----------------
 
 .. autofunction:: esper.switch_world
+.. autoattribute:: esper.current_world
 .. autofunction:: esper.delete_world
 .. autofunction:: esper.list_worlds
 .. autofunction:: esper.create_entity

esper/__init__.py

@@ -139,8 +139,15 @@ def process(self, *args: _Any, **kwargs: _Any) -> None:
 _get_component_cache: _Dict[_Type[_Any], _List[_Any]] = {}
 _get_components_cache: _Dict[_Tuple[_Type[_Any], ...], _List[_Any]] = {}
 _processors: _List[Processor] = []
-process_times: _Dict[str, int] = {}
 event_registry: _Dict[str, _Any] = {}
+process_times: _Dict[str, int] = {}
+"""A dictionary containing Processor timings.
+
+After each call to :py:func:`esper.timed_process`, the class name
+and elapsed call time (in millisections) for each Processor will
+be recorded in this dictionary. The times are replaced with each
+call.
+"""
 current_world: str = "default"
 """The name of the currently active World context.