Use request-deferred.el to fetch the query results

[galeo]

Hi @nathankot

I did some digging and it seems like the biggest bottleneck for company-sourcekit is actually the http response results being written into the sourcekit-output buffer. It takes a good ~2 seconds for 3k lines of output.

As you said, it may improve the performance without writing the query results into the *sourcekit-output* buffer. The code uses request-deferred.el to fetch the query results asynchronously and the returned response data is automatically parsed into JSON format. I also delete some code that becomes useless.

[nathankot]

@galeo

Thanks for the PR, this is awesome work 💯

Sorry for the slow responses (things have been really busy for me recently)

I checked out your branch and it is faster from my initial observations.
This also means we no longer depend on curl being available.

Lets see how this holds up as we go, I'll keep issue #24 open as there should be other places where gains can be made.