Implement /search

[bamos]

https://developer.github.com/v3/search/

Hi, sorry for filing this and #157.
I'd prefer to use the repository search api.

[bamos]

My currently (ugly) workaround for this is to
use egit-github's version of the search API and kohsuke/github-api
for everything else.
I'd prefer to only use one library, but egit-github doesn't support
all of the features of the repo/readme API.

This repo's well-written and documented, so I'd prefer to use it
for everything.
If I'm able, I'll take a look at the code and perhaps try implementing this myself.

[kohsuke]

Implemented toward 1.65.