Update pygments monkeypatch for compatibility with Pygments 2.0

[takluyver]

Closes gh-6877

I spent a while looking for a better way to achive this, to get rid of the monkeypatch, but none occurred to me, so I went with Carlos' suggestion of just updating it.

[ccordoba12]

I think there's no way out of this one because one of the limitations of the Pygments RegexLexer is that only works on one line at a time. I discovered that while trying to use it to highlight rst files in Spyder.

So +1 from me.

[takluyver]

I think pygments can handle more than one line, the tricky bit here is that the Qt console is only giving us one line at a time. I was looking into whether we could highlight the block as a whole, and concluded that there wasn't an easy way to achieve it.

It's also annoying that Pygments has an ExtendedRegexLexer which does allow this state to be stored externally without a monkeypatch - but only a handful of the lexers inherit from that, so there doesn't seem to be a practical way to use it as we want.

[ccordoba12]

Ups, sorry. Then the problem is with highlightBlock in Qt. I didn't remember which one was the culprit.