add support for res.json and binary data cache

[evanshortiss]

Currently the module only caches on the use of res.send and has issues with binary files and JSON. This PR should help resolve such issues, but might need a little more work.

Tests now use supertest rather than a spawned process, I found this easier to work with. Let me know your thoughts!

Caching occurs on data passed to res.socket.write, not res.send now. This is is the main update that facilitates support for res.json and binary responses. Cached items now represent the data sent to the response stream too, so this is what gets written to the cache:

HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: text/html; charset=utf-8
Content-Length: 46
ETag: W/"2e-PQ7Dm+NYwzgkRT8czBTdcQ"
Date: Thu, 26 May 2016 03:26:57 GMT
Connection: keep-alive

Now is Wed May 25 2016 22:26:57 GMT-0500 (CDT)

One potential issue is the Date header is cached; we might need to work around this?

[evanshortiss]

I believe this will fix:

• Cached respone as [object Object] #40
• cache http response code #43
• Can't get binary content to be cached #51
• Type option seems to not be taken into account #52
• Cache should preserve original response status code  #54

The build is failing, but I can't see why. Should I be able to see the output? They pass locally so I'd need the Travis output to figure it out.

[evanshortiss]

This might not be required now, since the content-type is stored in the body

[evanshortiss]

I created a new set of module to handle this since I needed more features, it's express-expeditious.

Will leave this PR open in the event it is ever merged 👍

[rv-kip]

@evanshortiss, can you rebase and resolve conflicts?

[krazyjakee]

@evanshortiss I understand this is old as hell but can you redo this PR for the dev branch? It would be greatly appreciated.