[add] initial ScrollView

Supports the following props: `children`, `contentContainerStyle`,
`horizontal`, `onScroll`, `scrollEnabled`, `scrollEventThrottle`, and
`style`.

Fix #6

docs/components/ScrollView.md

@@ -1,6 +1,7 @@
 # ScrollView
 
-TODO
+Scrollable `View` for use with bounded height, either by setting the height of
+the view directly (discouraged) or by bounding the height of ancestor views.
 
 ## Props
 
@@ -11,27 +12,29 @@ Child content.
 **contentContainerStyle**: style
 
 These styles will be applied to the scroll view content container which wraps
-all of the child views. Example:
+all of the child views.
 
 **horizontal**: bool = false
 
-When true, the scroll view's children are arranged horizontally in a row instead of vertically in a column. Default: `false`.
+When true, the scroll view's children are arranged horizontally in a row
+instead of vertically in a column.
 
 **onScroll**: function
 
-Fires at most once per frame during scrolling. The frequency of the events can be contolled using the `scrollEventThrottle` prop.
+Fires at most once per frame during scrolling. The frequency of the events can
+be contolled using the `scrollEventThrottle` prop.
 
-**scrollEnabled**: bool
+**scrollEnabled**: bool = true
 
-When false, the content does not scroll. Default: `true`.
+When false, the content does not scroll.
 
-**scrollEventThrottle**: number
+**scrollEventThrottle**: number = 0
 
 This controls how often the scroll event will be fired while scrolling (in
 events per seconds). A higher number yields better accuracy for code that is
-tracking the scroll position, but can lead to scroll performance problems.
-Default: `0` (the scroll event will be sent only once each time the view is
-scrolled.)
+tracking the scroll position, but can lead to scroll performance problems. The
+default value is `0`, which means the scroll event will be sent only once each
+time the view is scrolled.
 
 **style**: style
 
@@ -40,20 +43,42 @@ scrolled.)
 ## Examples
 
 ```js
-import React, { ScrollView } from 'react-native-web'
+import React, { ScrollView, StyleSheet } from 'react-native-web'
 
-const { Component, PropTypes } = React;
+import Item from './Item'
 
-class Example extends Component {
-  static propTypes = {
+export default class App extends React.Component {
+  constructor(props, context) {
+    super(props, context)
+    this.state = {
+      items: Array.from({ length: 20 }).map((_, i) => ({ id: i }))
+    }
   }
 
-  static defaultProps = {
+  onScroll(e) {
+    console.log(e)
   }
 
   render() {
     return (
+      <ScrollView
+        children={this.state.items.map((item) => <Item {...item} />)}
+        contentContainerStyle={styles.container}
+        horizontal
+        onScroll={(e) => this.onScroll(e)}
+        scrollEventThrottle={60}
+        style={styles.root}
+      />
     )
   }
 }
+
+const styles = StyleSheet.create({
+  root: {
+    borderWidth: '1px'
+  },
+  container: {
+    padding: '10px'
+  }
+})
 ```