Clarify that all these IE11 bugs have been fixed in IE12

[cvrebert]

Fixes #2.
Source: @gregwhitworth in #2 (comment)

[philipwalton]

I definitely agree that we should say if/when bugs are fixed in upcoming browser versions. The reason I didn't originally do this is I wasn't sure how best to present the information, and it didn't seem immediately pressing since none of the bugs are fixed in released browsers (with the exception of bug 6, which I just added today).

I've thought about it some more and here are my two favorite options:

1. Similar to what this pull request does, we list any fixes directly next to the affected browser, so it'd look like:

Browsers affected
Chrome 4-41 (fixed in 42+) Internet Explorer 10-11 (fixed 12+)

2. Or we could add a separate column. I can't decide if this would make it more or less clear:

Browsers affected	Browsers fixed
Chrome 4-41 Internet Explorer 10-11 (fixed 12+)	Chrome 42+ Internet Explorer 12+

What do you guys think?

If we do option 2, we should probably then move the tracking bugs below "Workaround" under their own heading.

[cvrebert]

I slightly favor (1), but either approach seems fine.

[philipwalton]

I think I do to. I'll merge this in and then make the minor changes myself.