Removed limit of 23 bytes for the client id.

Closes #82.
Removed two possible race conditions for offline messages.

The race conditions were:
1. the restoration of all subscriptions was done after connack, which
   means that there was a tiny window were a message could be lost.
2. the puback for a QoS 1 packet was sent before the write was
   concluded.
Bumped v0.15.0. Updated HISTORY.

Closes #73.
Fixes a missing quote in the README

A bullshit pull request but none the less.
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Contributed by Sam Beck (two-thirty.tumblr.com)
Merge pull request #83 from FaisalAbid/patch-1

Fixes a missing quote in the README
Merge pull request #84 from FaisalAbid/logobranch

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Adding the persistence part of the config in the README.

Closes #85.
Fixed doc typo persistance in persistence.
Fixed a typo in the config example in the README
Moved contributing section into the CONTRIBUTING.md file. Added CLA.
Sample Dockerfile.
Fixed Dockerfile. Missing instructions.
Added docker docs.
Better docs for Docker and test.mosca.io.
Merge pull request #86 from mcollina/docker

Docker support
Better Docker documentation.
merged