Multiple quoted tags

This is a bug @thatbettina and I came across when tags are entered using quotes, and there are multiple of them after one another, then things don't work as expected.

This PR adds a test case and a fix.

The problem is  that the regular expression that matches quoted tags matches a delimiter at the start and at the end. Because of this, when matching multiple consecutive quoted tags, the delimiter in between is already matched as end-delimiter for the first tag, and so can no longer serve as start-delimiter for the second tag.

By using zero-width lookahead in the regexp, the second delimiter is not consumed.

The PR also limits the Rails version again to >= 3.0, < 4.0 because we got unrelated errors when testing on Rails 4, so we couldn't verify the feature works otherwise. This also seems to be why the build on Travis is currently broken.