Better status messages and reliability

Added

• configuration for redis connection pool size (#57)
• merge.optimistic_updates configuration to prioritize updates over status checks (#64)
• Internal rate limiting of API calls to Github (#70)
• Improve status check messages when PR is being merged (#72)
• Add queue position information to status messages (#74)
• Display more information in status checks (#77, #112)
  • has blacklist labels reports the blacklist labels
  • invalid merge method displays the configured merge method and the valid merge methods
  • blocking review shows first blocking user
  • missing required review count shows review count and required review count
  • failing required status checks displays the failing status checks
  • waiting on status checks now reports the status checks we are waiting for
• Display status messaging for missing branch protection (#78)
• Add merge.message.strip_html_comments configuration option to strip comments from (#80)
  • This is useful for stripping HTML comments created by PR templates when the markdown body_type is used.
• Add require_automerge_label to configure requirement of automerge_label for working on PR (#82)
  • This overrides and disables notify_on_conflict (#86)
• Add status message warning for unsupported requiresCommitSignatures branch protection configuration (#90, #91)
  • This is a limitation of the Github API as Kodiak is not able to created signed commits when merging a PR.
• Add status message reporting of update branch failures (#94)
• Add "Known issues" section to README (#105, #114)
• Add 'empty' configuration option for merge.message.body to truncate PR body on merge (#111)
• Display configuration parsing errors with details page when kodiak cannot parse a configuration file (#116, #125)

Fixed

• Support PRs in draft state (#68)
• Fix bug where require_automerge_label would trigger kodiak to make an infinite loop of comments (#86)
• Fix poor status message templating on update branch failure case (#110)