Support multipart resources

[roll]

Overview

With specs-v1 resource file could be split into chunks. For now this functionality is missing in the lib. It requires some research to understand how it could be done in javascript.

Plan

• support multipart resources in resource.createByteStream internal function
• pass to tableschema.Table a stream with multipart contents

[rufuspollock]

@roll in the browser I'd suggest omitting this support. In node itself this is fairly easy - you just concat the streams ...

[roll]

@rufuspollock
thanks!