Arrays of structs, closures, and pattern matching as an expression

A litter/breed name, optionally []-suffixed, is now a real prop/purr param or return type (DocEntry[] entries is a real Vec ); closure literals (|param, ..| expr) lower to real Rust closures for .filter()/.map(); pounce> now also works as an expression, unwrapping a Result-shaped value and returning it in one step. The Language reference page's search box is now real, built from exactly these…