Store github authorization token globally

Fixes #33

Changes:
* move oauth authorization token from local git config
  to ~/.config/gitx/github.yml for reuse across projects
bump version
DRY up use of paths
remove project name from token note
Fix mutating getter antipattern
Fix bug creating double authorizations

inline #authorization_request_options method since only used in one
place
Merge pull request #38 from thegarage/global-config

global-config