Added basic code search functionality

[palas]

I have added the functionality for searching code: https://developer.github.com/v3/search/#search-code

I had to make several of the fields of "Repo" optional, but I have updated the samples accordingly.

Finally, I added the sample Search/SearchCode.hs, to illustrate the functionality.

[jwiegley]

@nataren @maxpow4h How does this look to you guys? I leave merging of pull requests up to you now, to avoid disrupting anything you might have in progress.

[nataren]

I don't think we leave spaces between the inner type and the brackets ('[' and ']')

[nataren]

Hi @palas, thanks for the change, I added some comment to specific parts of the code. Also, please bump the version to 0.11 in the github.cabal file and rebase your changes to a single commit once we are done with the changes.

@jwiegley The change looks good, and it does not interfere with anything I am working on (which is related to Commits and Refs).

[palas]

Fixed. :)

[nataren]

@palas 👍 Thanks. Looks good. I just realized that since the kind of terms that can be in the q (query) parameter changes depending on the search end-point, it would be great to create a small DSL that let's you build those queries for the specific type of search; the benefit would be better discoverability and type safety. Probably a version 2 of this change.

@jwiegley 👍