Simplified generator system

[maxitg]

Changes

• This is a complete rewrite of the generator system.

• Old GenerateMultihistory syntax is removed.

• Instead, all generators have the format

  Generator[System[rules], param1 -> value1, ...] @ init

  Note that param1, etc. are symbols rather than strings. They have usage messages, etc. Also, one can use lists or associations instead, e.g.,

  Generator[System[rules], {param1 -> value1}, <|param2 -> value2|>, param3 -> value3] @ init

• Parameters are now declared separately from systems and generators.

• Systems need to declare a logical expression specifying which parameters can be specified. For example,

  Implies[MaxEvents || MaxDestroyerEvents, EventOrder]

  means that EventOrder needs to be specified if either MaxEvents or MaxDestroyerEvents are specified.

• Generators have predefined values for some parameters. E.g., GenerateSingleHistory sets MaxDestroyerEvents -> 1, which can no longer be changed.

Comments

• Apologies for a huge PR. There is a lot of refactoring here as all instances of GenerateMultihistory had to be changed.
• Ordering functions page is deleted for now but should return as a page for the EventOrder parameter once it is used somewhere.
• @daneelsan, unfortunately, it will break #643, but on the flip side, it should make it a lot easier to define parameters (as one does not need to think where to put them anymore).

Examples

• GenerateSingleHistory:

In[] := #["StatesList"] & @
 SetReplaceTypeConvert[{WolframModelEvolutionObject, 2}] @
  GenerateSingleHistory[MultisetSubstitutionSystem[{a_, b_} :> {a + b}], MaxEvents -> 4] @ {1, 2, 3}
Out[] = {{1, 2, 3}, {3, 3}, {6}}

• GenerateAllHistories:

In[] := #["ExpressionsEventsGraph", VertexLabels -> Placed[Automatic, After]] & @
 SetReplaceTypeConvert[{WolframModelEvolutionObject, 2}] @
  GenerateMultihistory[
    MultisetSubstitutionSystem[{a_, b_} /; a < b :> {a + b}], MaxGeneration -> 2] @ Range[3]

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This change is