Adding label endpoints

[half-ogre]

This PR adds all the label endpoints.

TODO

• https://developer.github.com/v3/issues/labels/#add-labels-to-an-issue
• https://developer.github.com/v3/issues/labels/#create-a-label
• https://developer.github.com/v3/issues/labels/#delete-a-label
• https://developer.github.com/v3/issues/labels/#get-a-single-label
• https://developer.github.com/v3/issues/labels/#list-all-labels-for-this-repository
• https://developer.github.com/v3/issues/labels/#list-labels-on-an-issue
• https://developer.github.com/v3/issues/labels/#remove-a-label-from-an-issue
• https://developer.github.com/v3/issues/labels/#remove-all-labels-from-an-issue
• https://developer.github.com/v3/issues/labels/#replace-all-labels-for-an-issue
• https://developer.github.com/v3/issues/labels/#update-a-label

Testing

• Unit tests for all endpoints
• End-to-end testing for all endpoints

[half-ogre]

@pengwynn: Do y'all have any interest in me adding end-to-end tests for the endpoints I'm adding that actually hit the API, and that are only run conditionally based on an environment variable?

[pengwynn]

@half-ogre Thanks for working through these. 💖 Would have gotten back sooner, but I was off the grid. ⛺

Do y'all have any interest in me adding end-to-end tests for the endpoints I'm adding that actually hit the API, and that are only run conditionally based on an environment variable?

Not quite sure I follow. It looks like you've wired up tests with the same pattern the other methods use, right?

[half-ogre]

@pengwynn This PR is ready for review.

Not quite sure I follow. It looks like you've wired up tests with the same pattern the other methods use, right?

I was talking about adding acceptance tests in addition to the unit tests, that actually hit the live API, but the friction and amount of change this would add makes this not something to talk about in the context of this PR, even if you were interested. So, never mind. :)

[Tonkpils]

👍 looking forward to these changes

[pengwynn]

Looks like some whitespace issues in some of the tests?

[pengwynn]

@half-ogre thanks for the patch! I saw some whitespace/alignment issues (maybe mix of tabs/spaces?). Once we fix those up this looks good. 👍

[half-ogre]

I saw some whitespace/alignment issues (maybe mix of tabs/spaces?

My bad. I ran go fmt and all should be well now.

[pengwynn]

🍰