Refactor ::tanzer::scgi::handler to react to SCGI socket events, not client socket events, for performance
Improve ::tanzer::message for better SCGI support

Changes:

    * Refactor [::tanzer::message parse] to better handle different types
      of newlines from remote services as needed

    * Make [::tanzer::message parse] more strict in validating response
      bodies generated by a CGI program

    * Make ::tanzer::scgi::handler be patient and wait for buffer to fill
      up before calling it quits

    * Remove -newline flag from [::tanzer::message new]
Improve request newline sequence detection

Changes:

    * Detect line break sequence used in request header based on the
      presence of a carriage return prior to the first newline

    * Find header boundary based on the line break sequence detected
Backport SCGI performance improvements to CGI handler
Don't try to parse empty message buffers