gh 1.3.1

• gh now accepts lower-case methods i.e. both gh::gh("get /users/hadley/repos")
  and gh::gh("GET /users/hadley/repos") work (@maelle, #167).

• Response headers ("response_headers") and response content
  ("response_content") are now returned in error conditions so that error
  handlers can use information, such as the rate limit reset header, when
  handling github_errors (@gadenbuie, #117).