v5.5.0

• #17 via #25: Instead of a read_headers function, cheroot now
  supplies a HeaderReader class to perform the same function.

  Any HTTPRequest object may override the header_reader attribute
  to customize the handling of incoming headers.

  The server module also presents a provisional implementation of
  a DropUnderscoreHeaderReader that will exclude any headers
  containing an underscore. It remains an exercise for the
  implementer to demonstrate how this functionality might be
  employed in a server such as CherryPy.

• #26: Configured TravisCI to run tests under OS X.