Items needing investigation or implementation for RuleDispatch 1.0

 * "predicate functions" -- inline a function or method call into a dispatch
   expression/criterion

 * "classifiers" -- provide a way to easily define an ordered classification of
   items of some type

 * "matching and binding" -- add ways to do pattern matching and binding
   dispatch expressions to variables that can then be used in a function body

 * removing rules from a dispatcher, either manually or automatically (as when
   an 'is'-based criterion becomes invalid due to GC of the target)

 * move from using "dispatch function" on criteria to using index/node classes

Documentation needed for dispatch package in RuleDispatch 1.0

 * Basics -- strategy.default, dispatch.on(), dispatch.generic(), Dispatcher,
   f.when()

 * Translation reference (in, is, isinstance/issubclass, etc.)

 * Dynamic construction -- Signature, Argument, Predicate, PositionalSignature,

 * Adding new criteria (ICriterion, expressionSignature, validateCriterion)
   [Issue: current mechanism needs to change to index/node classes; see above]

 * ast_builder (define IPyBuilder interface, finish constructs like for/lambda)

 * Misc. -- dispatch.as()

 * Implementation info
    'ProtocolCriterion', 'ClassCriterion', 'SubclassCriterion', 'Inequality',
    'AndCriterion', 'OrCriterion', 'NotCriterion', 'TruthCriterion',
    'Min', 'Max', 'Pointer', 'dispatch_by_truth',
    'IdentityCriterion', 'NullCriterion',
    'Call', 'ExprBuilder', 'Const', 'Getattr', 'Tuple',
    'OrExpr', 'AndExpr', 'CriteriaBuilder',