Fixes for id attar + add click attr for callback.

[developer88]

First of all - with the latest version of jqplot this directive is not working for me, because it call $(element).jqplot, but according to official jqplot's documentation there is only one appropriate way - $.jqplot('elemente's id' ....);
Second - I have added chart-click attribute to pass a function that will be called when event 'jqplotDataClick' is fired.

[developer88]

Smth wrong with Travis, but definitely, that is not my fault.

[wesleycho]

You should be able to just do elem.unbind - elem is normally a jqLite wrapped element, but with jQuery present, it will be a jQuery wrapped element.

[wesleycho]

I will fix these Travis errors tonight - other than these minor issues I've commented on, I like this PR, and am willing to merge this and tag a new release when this is tidied up.

[wesleycho]

It would be a good idea to keep a reference to $.jqplot(id, data, opts) cached outside the render function.

[wesleycho]

There should be a test added for the binding of the callback as well, to test that it properly sets the correct binding and unsets the old binding.

[wesleycho]

click_callback should be clickCallback, to maintain style consistency.

[tohyf]

Any time this fix will be finalized and committed ?