Lint to avoid putting newlines in links or variables

[tabatkins]

Request from a fellow Chromie: a lint that warns if you have broken a link or variable across lines, as that makes it harder to search for terms in the source later.

I should be able to do this now, by walking the document. I can possibly do it better with the parser rewrite, but I don't think I need to wait for that; it'll just give me better line numbers in the error.

[domfarolino]

I think I disagree with this change. The specs I work on generally follow the HTML Standard style guide, which allows for line breaks in between words in a dfn or link, or even within tags associated wtih those dfns or links. All of those specs will I guess just be broken now if they treat warnings as fatal? That seems bad and backwards incompatible.

[tabatkins]

Lints are always optional, and this would be default-off, like most of the lints are.