Modify line length checks to ignore certain cases

[andrewnicols]

Sadly I don't think that we can easily do this with configuartion of the existing sniff, but essentially there are certain errors and warnings we want to ignore with regards line length. For example, when writing a Behat step, it is not uncommon to end up with a particularly long @Given line, which cannot be broken apart.

Ideally we should ignore line length for certain tags, including Given, When, Then, and others.