Uses a CapacityLimiter on trio instead of a Semaphore

[miracle2k]

Those two are not identical:

import trio

async def main():
	c = trio.Semaphore(10)
	async with c:
		print('one in')
		async with c:
			print('two in')

trio.run(main)

one in
two in

but:

import trio


async def main():
	c = trio.CapacityLimiter(10)
	async with c:
		print('one in')
		async with c:
			print('two in')


trio.run(main)

one in
RuntimeError: this borrower is already holding one of this CapacityLimiter's tokens

This means that I cannot open two connections in the same task https://github.com/Fuyukai/riopg.

[theelous3]

Ooo! Nice lib. Didn't realise F was making this. Neato.

Switched and updated.