Add repository settings to configure PR merge methods

[ryangribble]

Fixes #1475

• Add new options to Get Repository methods
• Poke API to figure out whether any of the GetAll (for Current, Public, For Organization, etc) methods return these new fields (despite API docs not mentioning it) and implement if so

(confirmed no other methods like GetAllForCurrent, GetAllPublic, GetAllForOrg return the new fields even when accepts header is provided, so only the individual Get Repository call needs to be implemented)

• Add new options to Create Repository request
• Add new options to Edit Repository request
• Waiting for github support to advise regarding Create Repository call still not appearing to support the new fields

(support confirmed this was a documentation error and Create Repository call does not support these parameters)

I've had to contact GitHub support as the new fields aren't actually being returned but I'm pretty sure everything is correct on my side...

[ryangribble]

Github support replied and confirmed there was some upstream problems which they've pushed fixes for.

With those fixes, the Get and Update integration tests I added are now passing 👍

Still seems to be an issue with Create call which I've asked support to look into

[ryangribble]

Support reply regarding create method:

Turns out that this isn't a problem in the code, but the documentation -- it was originally intended for the feature to be supported by the endpoints to fetch and modify a repository, even though the documentation says it should be supported by the endpoint for creating a repository (the documentation shouldn't have said that). We'll be updating the documentation to reflect this.

So I'll remove the create method tomorrow then this PR can be merged

[ryangribble]

OK this is now good to go, I've removed the CreateRepository changes, but left the commit in the history incase github do end up supporting it, we can resurrect it

[shiftkey]

I'm impatient and Travis is having issues

#yolo