Reworking of grape streaming response support

[Edward Rudd]

Hey all,

A PR I had been working on for a bit was merged in today that reworks the streaming response support in Grape.

PR:  https://github.com/ruby-grape/grape/pull/1520

This makes a few changes

1) deprecates file

file is now fully deprecated and should not be used.  The functionality has now been replaced with sendfile

2) add sendfile (to replace file)

sendfile better clarifies the intention of utilizing the sendfile support in the how web server.  This should be used with a file path to send a file directly.

3) adjustments to stream

Stream now supports strem-like objects again.  Just pass an object instance that responds to :each and you can stream data back to the client.  e.g. send paginated results from a database.

I'd like the community to comment, test, and verify the change I made.

Thanks,

Edward