Run YamlLint against IDL files

In order to enforce consistency across the IDL files, YAMLLint can be used to verify column
limits, and spacing around ":" for instance.

Resources
https://yamllint.readthedocs.io/en/latest/
https://pypi.python.org/pypi/yamllint
https://github.com/adrienverge/yamllint

Example config file:

extends: default

rules:

  line-length:

    max: 100