updated documentation for addJavaScriptHandler method, updated README.md, updated inline webview example

added return value for JavaScriptHandlerCallback, added flutterInAppBrowserPlatformReady event for javascript, breaking change: javaScriptHandlersMap contains only one callback

upgrade to androidX

added support for iOS inline native WebView integrated in the flutter widget tree (#18, #45), fix #54 #38 #26 #32 #33 #29 #15

Fixed bug where passing null to expiresDate failed

[fix] encode resourceURL

Fixed error: Double value cannot be converted to Int because the result would be greater than Int.max in 32-bit devices

fixing a problem in safari webview and adding tabs to examples

added WebHistory and WebHistoryItem class, added getCopyBackForwardList, goBackOrForward, canGoBackOrForward and goTo methods for InAppWebView and InAppBrowser, updated docs