koajs/koa — pull request #326 by dead-horse (2014-08-04 03:45:46+00:00)
Title: alias request.headers as request.header

it is natural to use `this.request.headers` to get the header object because original node request use `headers`.

and in express, `req.header` is alias as `req.get`. but in Koa, it delegate `req.headers`, maybe it will confuse users who use express before.