release v0.56.0

fixed websocket-client#471

add Change Log

revert websocket-client#442

Merge pull request websocket-client#460 from hugovk/rm-3.3

Update supported Python versions (2.6, 2.7, 3.4+)

fixed websocket-client#432

fix format

add document

Merge branch 'master' of https://github.com/websocket-client/websocke…

…t-client