Corrected a submodule URL
Ensure a valid github profile is chosen.

I was seeing the following error when I had more than one github profile:

    Invalid slot type: gh-gist-api, :base, string, nil

I tracked it down to this completing-read not requiring valid input.
This change makes it so:
* If the user inputs nothing, it returns the first profile in the list.
* The choice must be in the list of profiles.

Meanwhile, for people using ido-ubiquitous, this is also an acceptable
workaround:

(setq ido-ubiquitous-enable-old-style-default nil)
added basic docs for issues
Add support for Pull Request comments API.

Related: https://developer.github.com/v3/pulls/comments/
Merge pull request #43 from areina/add-support-for-pr-comments-api

Add support for Pull Request comments API.
Merge pull request #42 from nicferrier/master

added basic docs for issues
Merge pull request #39 from RenWenshan/master

Corrected a submodule URL
Merge pull request #40 from mrwacky42/master

Ensure a valid github profile is chosen.