extmod/asyncio: Rename uasyncio to asyncio.

The asyncio module now has much better CPython compatibility and
deserves to be just called "asyncio".

This will avoid people having to write `from uasyncio import asyncio`.

Renames all files, and updates port manifests to use the new path. Also
renames the built-in _uasyncio to _asyncio.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

extmod/asyncio/__init__.py

@@ -0,0 +1,31 @@
+# MicroPython asyncio module
+# MIT license; Copyright (c) 2019 Damien P. George
+
+from .core import *
+
+__version__ = (3, 0, 0)
+
+_attrs = {
+    "wait_for": "funcs",
+    "wait_for_ms": "funcs",
+    "gather": "funcs",
+    "Event": "event",
+    "ThreadSafeFlag": "event",
+    "Lock": "lock",
+    "open_connection": "stream",
+    "start_server": "stream",
+    "StreamReader": "stream",
+    "StreamWriter": "stream",
+}
+
+
+# Lazy loader, effectively does:
+#   global attr
+#   from .mod import attr
+def __getattr__(attr):
+    mod = _attrs.get(attr, None)
+    if mod is None:
+        raise AttributeError(attr)
+    value = getattr(__import__(mod, None, None, True, 1), attr)
+    globals()[attr] = value
+    return value