Use Feature Detection instead of Browser Sniffing

[willsp]

While the previous implementation used feature detection, it was using it wrong. It was, essentially using feature detection as a more advanced browser sniffer.

• Updated this to detect the features actually being used to measure zoom.
• Moved the functions to the same place as the checks, to make it easier to keep the 2 connected.
• Made some adjustments so it passes jshint.
• This fixes a bug with iOS8 Safari.

[bradvogel]

This unfortunately doesn't work within iframes.

[willsp]

Ah, that's not cool... Not really a use case for us. Did the original work with iframes?

If you have any suggestions (or better yet, code), let me know and I'll see if I can make it work...

[bradvogel]

Never tried the original. Seems to be a couple of years out date. Lack of iframe support shouldn't prevent you from merging though - this PR is still very useful! I'll look into adding support for iframes.

[ericsaboia]

any updates on this?

[willsp]

@ericsaboia Nope... Sorry. I'm no longer using it, so have little reason to get it working for iframes. If you fix it and submit a pull request to my fork, I'll merge it.