[TIMOB-13160] Missing HTTPClient state constants / Outdated documentation

Problem description

I've been trying to use the Titanium.Network.HTTPClient constants for readyState, using code such as Titanium.Network.HTTPClient.DONE inside the onreadystatechange event, as shown [in the documentation](http://docs.appcelerator.com/titanium/3.0/#!/api/Titanium.Network.HTTPClient-property-readyState) and in this [old tutorial](https://wiki.appcelerator.org/display/guides/HTTPClient+and+the+Request+Lifecycle), that's using hardcoded numbers instead of the constants. However, those constants are always undefined. Did they exist and were later removed and the documentation was left there, or is this some sort of bug, that's hiding the constants out of our view? I've originally created a [question on the Q&A site](http://developer.appcelerator.com/question/149715/how-to-use-tinetworkhttpclientonreadystatechange) that then prompted me to create this report.