Add consumer api

README.md

 ```js
 import React from 'react';
 import { View } from 'react-native';
-import { SafeAreaProvider, useSafeArea } from 'react-native-safe-area-context';
-
-function SomeComponent() {
-  const insets = useSafeArea();
-
-  return <View style={{ paddingTop: insets.top }} />;
-}
+import { SafeAreaProvider, SafeAreaConsumer, useSafeArea } from 'react-native-safe-area-context';
 
 function App() {
   return (
     <SafeAreaProvider>
-      <SomeComponent />
+      <HookComponent />
+      <ClassComponent />
     </SafeAreaProvider>
   );
 }
+
+// With hooks
+function HookComponent() {
+  const insets = useSafeArea();
+
+  return <View style={{ paddingTop: insets.top }} />;
+}
+
+// With consumer
+class ClassComponent extends React.Component {
+  render() {
+    return (
+      <SafeAreaConsumer>
+        {insets => <View style={{ paddingTop: insets.top }} />}
+      </SafeAreaConsumer>
+    );
+  }
+}
+
+
 ```

src/index.tsx

   fill: { flex: 1 },
 });
 
+export const SafeAreaConsumer = SafeAreaContext.Consumer;
+
 export function useSafeArea(): EdgeInsets {
   const safeArea = React.useContext(SafeAreaContext);
   if (safeArea == null) {