bottom_navigation_bar library

modify from https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/material/app_bar.dart lastest push: 2019.12.29 flutter v1.13.5

lastest commit: 2019.11.28 commit https://github.com/flutter/flutter/commit/449f4a6673f6d89609b078eb2b595dee62fd1c79 #45375 https://github.com/flutter/flutter/pull/45375

Classes

BottomNavigationBar
A material widget that's displayed at the bottom of an app for selecting among a small number of views, typically between three and five. [...]