Configuring stream reader buffer limit.

[PeterQFR]

Whilst passing images around via PyTAK, I ran into a limitexception on the rxreader generated from the protocol factory.

This generally happens if the asyncio.readuntil doesn't reach the delimiter before the limit is reached.

It doesn't seem PyTak is enabling this to be configured and its set at the asyncio defaults of 2 ** 16 or 64KB. https://github.com/python/cpython/blob/b61fece8523d0fa6d9cc6ad3fd855a136c34f0cd/Lib/asyncio/streams.py#L23

I was able to increase this by increasing the limit directly in pytak/client_functions.py line 220 by specifying the limit. Here I set it to 4GB, I haven't run into the limit error.
eg

reader, writer = await asyncio.open_connection(host, port, limit=(2 ** 32)

Would it be supported to increase this limit or make it configurable?