Add Processor::{Evaluator, Pivot, Wrapper}

Supports the following chain definition ootb now:

env = Substation::Environment.build do
  register :evaluate, Substation::Processor::Evaluator
  register :call,     Substation::Processor::Pivot
  register :wrap,     Substation::Processor::Wrapper
end

AUTHENTICATED = env.chain { authenticate }
AUTHORIZED    = env.chain(AUTHENTICATED) { authorize }

CREATE_PERSON = env.chain(AUTHORIZED) do
  evaluate Sanitizers::NEW_PERSON
  evaluate Validators::NEW_PERSON

  call Actions::CreatePerson

  wrap Presenters::Person
  wrap Views::Person
end