file API

好的教程：http://blog.csdn.net/fwwdn/article/details/8349657/

FileEntry and DirectoryEntry

FileList : file集合，（length，item）

Blob ： slice(), (size, type) 

File : (name, type, lastmodifiedDate, lastModified)

FileReader : 

void readAsArrayBuffer(Blob blob);
void readAsBinaryString(Blob blob);
void readAsText(Blob blob, optional DOMString encoding);
void readAsDataURL(Blob blob);
abort(): 停止读取

FileError, FileException, FileUpload, DateTransfer