Implement hub api --paginate

[mislav]

REST resources are paginated by following the <next> link in the "Link" response header.

A GraphQL query has to accept the optional endCursor string variable and output pageInfo:

pageInfo {
  hasNextPage
  endCursor
}

Full GraphQL example: find all repositories owned by USER:

hub api --paginate graphql -f owner="USER" -f query='
  query($owner: String!, $per_page: Int = 100, $endCursor: String) {
    repositoryOwner(login: $owner) {
      repositories(first: $per_page, after: $endCursor, ownerAffiliations: OWNER) {
        nodes {
          nameWithOwner
        }
        pageInfo {
          hasNextPage
          endCursor
        }
      }
    }
  }
'

https://developer.github.com/v3/#pagination
https://developer.github.com/v4/guides/resource-limitations/#node-limit