PING causes receive() problems

Nobody has claimed this yet.

A bit surprising, this is _not_ about #14. I don't care about "proper" implementation of ping/pong but am having problems because the ws server (which is beyond my control) sends a ping on connect and the client on my side reads 1 byte too many and the frames on my side got royally screwed up from there on.

The problem is around here: https://github.com/lipp/lua-websockets/blob/master/src/websocket/sync.lua#L14
The first chunk read apparently is always of size 3 - but it turns out PING is a frame of only 2 bytes.

On example i tracked with wireshark, the first chunk read is "89 00 82", which gets returned to me as an empty message (which is fine by me) - however turns out the PING is actually "89 00" and the 82 is part of the next frame "82 0b ..." (11 byte binary frame). Because 82 was mis-read, the 2nd frame turns into "0b ..." and everything goes downhill afterwards.

Seems that simply changing that line to `bytes = 2` might be okay, given a quick skim at frame.decode() - but is that so?

ps. also `bytes = 2` on line 60

Start at src/websocket/sync.lua lines 14 and 60, then read the related frame.decode() handling. Reproduce the reported sequence where a two-byte PING is followed by an 11-byte binary frame, and verify that reads preserve both frame boundaries without consuming the next frame's first byte.

Written by the indexing model from the issue text.