Stapling Plier

• Improved consistency in source code.
• Improved exception handling.
• Add an argument that tells stapled to parse a HAProxy config file for
  sockets and certificate directories.
• It is now possible to specify single certificate aside from entire
  directories.
• DEPRECATED: --directories was superseded by --cert-paths.
• Improve the stability of the socket communication.
• Add a time stamp to the log output.
• Reduce the noise for log level INFO.
• Fix an edge case where HAProxy is not aware of staples that are still valid
  and where stapled decides fetching new ones is not necessary.
• Fix recursive mode when used with HAProxy sockets, there is no practial
  use case for this and it is still not supported but it won't cause an
  exception anymore and manual testing can be done in recursive mode now.
• Fix various typo's in documentation.
• Improve documentation of the config file.
• Add note about HAProxy's stapling perculiarities in README and
  documentation.