shims for Web APIs (core-web)

core-web, 类似 core-js 和 polyfill.io 的项目，意在整理所有 Web APIs 的相关 shim 以及 polyfill 。

目前第一版实现了以下 APIs：

stable (natively supported above IE10):

• Blob (constructor, stream, arrayBuffer, text)
• Event (preventDefault, stopPropagation)
• EventTarget (addEventListener, removeEventListener)
• File (constructor)
• FileReader (constructor)
• FormData
• Global (atob, btoa, console)
• HTMLElement (focus)
• HTMLOptionElement (Option)
• URL (constructor, URLSearchParams)
• XMLHttpRequest (send)

featured (natively unsupported under IE):

• Streams (ReadableStream, WritableStream)
• Text (TextEncoder, TextDecoder)