Merge pull request #26 from hintjens/master

Changes to RFCs as part of stabilising ZMQ/4.0
Merge pull request #27 from hintjens/master

Various updates to draft RFCs
Add initial draft of SRP spec
Merge pull request #28 from PSG-Sakari/master

Add initial draft of SRP spec
Added new RFC for FileMQ v2
Added new RFC for FileMQ v2