Use io.open() when reading files in cli which has the same behaviour
in Python 2 and Python 3, and supply the newline='' parameter which
handles but does not translate line endings.
Add dos.yml test file with windows newlines.
Also add to file finding test expected output.
Add test for new-lines rule through the cli.
Validates files are read with the correct universal newlines setting.
Fixesadrienverge/yamllint#228