ERBHandler evaluates an ERB file and returns the result.  This handler is automatically used if there are .rhtml files in a directory served by the FileHandler.
ERBHandler supports GET and POST methods.
The ERB file is evaluated with the local variables servlet_request and servlet_response which are a WEBrick::HTTPRequest and WEBrick::HTTPResponse respectively.
Example .rhtml file:
Request to <%= servlet_request.request_uri %> Query params <%= servlet_request.query.inspect %>
Creates a new ERBHandler on server that will evaluate and serve the ERB file name
 
               # File webrick/httpservlet/erbhandler.rb, line 42
def initialize(server, name)
  super(server, name)
  @script_filename = name
end
             
            Handles GET requests
 
               # File webrick/httpservlet/erbhandler.rb, line 50
def do_GET(req, res)
  unless defined?(ERB)
    @logger.warn "#{self.class}: ERB not defined."
    raise HTTPStatus::Forbidden, "ERBHandler cannot work."
  end
  begin
    data = File.open(@script_filename, &:read)
    res.body = evaluate(ERB.new(data), req, res)
    res['content-type'] ||=
      HTTPUtils::mime_type(@script_filename, @config[:MimeTypes])
  rescue StandardError
    raise
  rescue Exception => ex
    @logger.error(ex)
    raise HTTPStatus::InternalServerError, ex.message
  end
end