Add descriptions support for the nodes: ExampleTable, Outline and Sce…

[jojo1981]

Now the descriptions.feature sample in CompatibilityTest will work. The code is backward compatible.

[ciaranmcnulty]

This looks great! How does it change the output of the pretty printer in Behat, though? As long as it's just that the descriptions are cleanly omitted I think that's fine?

[stof]

This might impact the pretty printer ignoring description because previously, that description would be parsed as a multi-line title (and so displayed). However, adding the rendering of the description in Behat should be easy.

[jojo1981]

I didn't check that, but as this change is not backwards compatible based on functionality a new major version should be released including this feature. The Behat library can be made compatible later and use the new major version of this library.