add option_fold

add binomial_ge_n_over_k_pow_k

removed tool that was never finished

added file headers

updated MaSh doc

moved MaSh's Python code into Isabelle

updated NEWS etc.

distinguish declated tfrees from other tfrees -- only the later can be optimized away

clarified status of Legacy_XML_Syntax, despite lack of Proofterm_XML;

reset active areas on content update;

more general sendback properties; support for padding of line boundary, e.g. for ad-hoc insertion of commands via 'help';

tuned command descriptions;

refined outer syntax 'help' command;

tuned signature;

always reset active areas;

no special treatment of control_reset, in accordance to other control styles;

tuned signature;

tuned signature;

tuned signature;

tuned signature; uniform view.fontsize fallback;

renamed main plugin object to PIDE;

tuned signature -- avoid intrusion of module Path in generic PIDE concepts;

explicit module UTF8;

tuned file name;

Isabelle-specific implementation of quasi-abstract markup elements -- back to module arrangement before d83797ef0d2d;

prefer strict error;

quasi-abstract module Rendering, with Isabelle-specific implementation;

added convenience actions isabelle.increase-font-size and isabelle.decrease-font-size;

eval PDF_VIEWER/DVI_VIEWER command line, which allows additional quotes for program name, for example;

retain hidden_color (i.e. transparent white) instead of replacing it by semantic text color, to make control symbols more hidden and avoid "dirty" lines with some fonts;