API clean-up

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Clean up the framework.

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• Rename Map. CSP::System maybe?
• Get rid of CSP::Alternation::List
• Could CSP::Process inherit Fiber?
• Should CSP::Channel inherit Queue?
• Figure out what to do with the channel input and output names, which is really confusing currently.

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• Make CSP::Process the process definition (that can be subclassed), and create some other class for holding a Process 'instance'.

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• Should some of the blocks be run in a context class to avoid the block parameter?