Add shield.io status buttons to README file
Add shield.io status buttons to README file

Leave license button unused for the time being, as it will only work
once 1.0 is registered on PyPI.

pyeve/cerberus,dkellner/cerberus,nicolaiarocci/cerberus,funkyfuture/cerberus,pyeve/cerberus,dkellner/cerberus,funkyfuture/cerberus,nicolaiarocci/cerberus