chore(release): 3.1.0

chore(release): 2.1.0

feat: add support for Socket.IO v3

See also:

- https://github.com/socketio/engine.io-protocol#difference-between-v3-and-v4
- https://github.com/socketio/socket.io-protocol#difference-between-v5-and-v4

refactor: use correct Engine.IO protocol revision

The 3rd revision is included in Socket.IO v1/v2, whereas the 4th is
included in Socket.IO v3.

Note: this query parameter is not currently checked on the server-side

Reference: https://github.com/socketio/engine.io-protocol

Merge branch 'master' of https://github.com/socketio/socket.io-client…

…-cpp

add boolean message type, fix crash of a synchronization bug

breaking change of ack callback, windows compile fix for PR

fix wild reconnect after too many times

Merge remote-tracking branch 'origin/tls'

fix console demo compile issue in VS2012SP4