Deprecate .bind("ready") event

[dmethvin]

The "ready" event is error prone because users may attach an event handler after it has fired. It is much more natural for ready semantics to follow the Promise model; if handlers are added after the document is ready then they will fire. We're adding a ready Promise in 1.8 (see #11470) and of course the standard $(fn) or $().ready(fn) continue to work without change.

Let's deprecate the ready event as of 1.8; there is no hurry to remove it, but let's help users avoid dumb errors caused by dumb APIs.

[dmethvin]

Just to be absolutely clear what is being deprecated here, it is these forms:

$(document).bind("ready", fn);
$(document).on("ready", fn);

Where "ready" is a custom event name that is only fired once by jQuery when the document becomes ready.

[dmethvin]

Documentation updated.