Update README.md for simpler install instructions.
3.0 to 3.1 upgrading guide
[CB-4881] Change plugin to feature

- Change <plugin> to <feature> under <plugins-plist> section
[CB-4881] Update plugin to feature in plugin spec for edge.
[CB-3820] BackgroundColor works the same for Android/BB
[CB-3820] resolve discrepancy in BB's orientation values
[CB-3820] AutoHideSplashScreen is iOS only
[CB-3820] DisallowOverscroll concerns rubber-band, not glow
strip potentially buggy nested XML comments
[CB-3820] HideKeyboardFormAccessoryBar is for iOS & BB
[CB-3820] clarify scaope of current page: non-platform-unique content
[CB-3820] whether HideKeyboardFormAccessoryBar applies to >1 input matters little
[CB-3820] function of TopActivityIndicator is now clear
[CB-3820] clarify MediaPlaybackRequiresUserAction's effective scope
[CB-3820] query re loadingDialog & loadingPageDialog usage not important
[CB-3820] correction: icon/splash mechanism is PGB-only
[CB-3820] rm PGB-specific content
[CB-3820] rm PGB-specific icon/splash content
[CB-3820] PGB's splash-screen-duration => CV's SplashScreenDelay
[CB-3820] removed deprecated UseBrowserHistory pref