adapt examples to new intermediate typedef

joint work with blanchet: intermediate typedef for the input to fp-operations

prefer abstract datatype -- in accordance to ML version;

tuned data structure;

tuned;

tuned comment;

tuned signature;

tuned errors -- in accordance to Scala version;

tuned errors -- in accordance to ML antiquotations;

more explicit method reports; avoid combinator parsers with observable effect -- unreliable due to backtracking (Scan.FAIL) and incremental input (Scan.MORE);

merged

tuned whitespace; tuned proofs;

tuned whitespace; modernized theory setup;

clarified init_models: simultaneous initialization of all document models, before flushing edits by regular means (via PIDE.editor.invoke) -- important for consolidated doc_blobs when determining initial edits; clarified asynchronous event propagation: determine buffers where they are actually accessed; tuned signature;