replace asyncio event loop with uvloop's implementation

[mgxd]

Something to consider: MagicStack/uvloop

uvloop makes asyncio 2-4x faster

[effigies]

We could use it opportunistically:

try:
    import uvloop
    has_uvloop = True
except ImportError
    has_uvloop = False

...
if has_uvloop:
    uvloop.install()
asyncio.run(...)

[satra]

i'm not sure speed is a key concern at this point. however, we can follow @effigies suggestion to use it opportunistically. it won't be installed by default, but if you do, we can use it. i know sanic uses it.