Links a process under a participant [name].

Turns top level processes into participants

Some examples :

    require 'engine/participants/participants'

    engine.register_participant(
        "transmit_to_accounting",
        "http://company.process.server.ie/processes/acc0.xml")

    engine.register_participant(
        "hr_resume_review_process",
        "file:/var/processes/hr_resume_review_process.rb")

Some more examples :

    class RegistrationProcess < OpenWFE::ProcessDefinition
        sequence do
            participant :ref => "Alice"
            participant :ref => "Bob"
        end
    end

    # later in the code ...

    engine.register_participant("registration", RegistrationProcess)

Or directly with some XML string :

    engine.register_participant("registration", '''
        <process-definition name="registration" revision="0.1">
            <sequence>
                <participant ref="Alice" />
                <participant ref="Bob" />
            </sequence>
        </process-definition>
    '''.strip)

It‘s then easy to call the subprocess as if it were a participant :

    sequence do
        participant :ref => "registration"
            # or
        participant "registration"
            # or simply
        registration
    end

Note that the ‘subprocess’ expression may be used as well :

    sequence do
        subprocess ref => "http://dms.company.org/processes/proc1.rb"
    end

But you can‘t use the URL as an expression name for writing nice, concise, process definitions.