add option autoEnd to enable append customized data after pipe

[xdcarter]

add option autoEnd to give chance to append some customized data to the raw file。in the case of package tool, I want to auto add the module wrapper code to the raw JS in dev mode，to avoid the trouble for the package building。

[dougwilson]

Thanks for adding docs! I didn't really look over it at the time, but I saw you added the docs, and went to look. It made we wonder why would you add the autoEnd option to the main options instead of accepting the option through our .pipe() method, especially since it looks like the intention is to mimic the .pipe() option from Node.js core? Seems like updating the PR to just be .pipe(res, { end: false }) to match .pipe() from core streams would make the most sense.

[xdcarter]

Cuz I cannot add my new commit to the existed pull request #135, I have to close #135 and open new PR for your review. At this moment, I have no change request to make. Would you pls review #137 and see if it can be merged to master?