Slimmage Background Image plugin

[protherj]

This is my first attempt at a Background Images plugin based on the Pull Request #37 from dancek. Slimmage has changed considerably and I hope I got it generally right.

Note: see the thread for Pull Request #55 for more background.

[protherj]

How do I fix the Travis CI build issues?

[erikbra]

Looks like performance issues, if I interpret the log correctly (red timings), or am I wrong?

[lilith]

First we need to fix the existing problems. Then we can address this PR by adding associated tests for the new functionality.

[wiedikerli]

@nathanaeljones whats the status of this pr?

[ProNotion]

This is working great for me so far - thanks Jason. The only issue of slight concern is the lack of fallback like we have with

[wiedikerli]

@nathanaeljones any plans to merge this pr?

[firthy]

@nathanaeljones I'd like to see this PR as part of the plugin also

[lilith]

Slimmage.js tries to do a very difficult thing. 99% of possible techniques fail on at least 1 crucial browser. This is not a space where I can merge pull requests for features which don't have associated unit tests. The chance of any new feature working across the same set of browsers is miniscule, in general.

I can't merge this without tests, and I don't have the resources to fix the bitrot in the existing tests. If someone wants to tackle #58, I hand out write access quite readily. Once #58 is fixed, then tests can be added to this PR and (if they pass), it can be merged.