Comments and fixes

Added many comments to explain plugin flow, function and settings. Fixed
some old utility funciton (like getSetupFunctions, previously
getRelatedFunction). Changed some settings type, removed onPageUnload
and onPageLoad (collapsed into onLoad and onUnload).
Added requestJsonp and additionalRequestHeaders as Salvo suggested.
[Thank you so much]

Now jBridge make XHR GET requests instead POST.