Custom Github Host

[mtchavez]

Purpose

Github Enterprise has different API endpoints for running on your own custom domain. Allowing the user to customize the Github API host endpoint allows someone to use gethub with their own Enterprise Github.

Changes

Go build errors

I was unable to build using go 1.3 or 1.4 and had to do the following

• Move version into constant in main.go
• Move usage() func to main.go

  Host changes

• Ask for github host on authorization
• Save host to multistep state
• Write host to config file
• Update API calls to use configured host
• Default to https://api.github.com

[pearkes]

LGTM! Nice.