`send_frame` interface does not return anything.
readability++
Tests for `is_valid_close_code`.
Remove ConnectionClosed exception as code path code path for handling
closing the websocket.
Ensure `None` is handled correctly with `encode_bytes`
bytes -> bytestring
Doc update
Doc update
Move test helpers into it's own module.
Tests for `pixie.upgrade_connection` for protocol versions 75/76
Set the correct WebSocket-Location header based on the hixie version.

hixie-75 sets WebSocket-Location
hixie-76 sets Sec-WebSocket-Location
Split upgrade connection tests in to protocol versions