misc tuning and clarification;

clarified markers for syntax consts: avoid overlap with logical consts;

update ci mail address;

minor performance tuning;

notable performance tuning (amending a59d9b81be24 and 8976c5bc9e97): avoid costly could_beta_eta_contract, which traverses the whole term; always use Item_Net.retrieve instead, but on frozen TVars/Vars to enforce matching instead of unification;

tuned;

clarified signature;

tuned whitespace;

support multiple positions (non-empty list);

more robust syntax translation;

clarified concrete vs. abstract syntax;

more inner-syntax markup;

clarified concrete vs. abstract syntax;

clarified concrete vs. abstract syntax;

more operations;

tuned;

tuned signature;

more operations;

more accurate treatment of constraints: restrict permissive mode to output;

tuned;

tuned proofs;

clarified order of tooltips: make it less dependent on report order from ML (which differs for input vs. output);

clarified signature (see also 1de8a8b1ae79);

clarified signature;

more type information; clarified signature;

more type information;

clarified signature;

clarified signature;

tuned signature;

clarified signature;

suppress dummyT, e.g. from Type_Annotation.print;

tuned proofs;

print type constraints for consts with mixfix syntax;

tuned comments;

obsolete (see 137ea3d464be);

tuned proofs;

tuned whitespace;

more inner-syntax markup;

less instrusive rendering for input buffer (in contrast to 264f043c5da1);

clarified inner-syntax markup;

tuned whitespace;

tuned whitespace;

clarified syntax declarations: keep things together;

tuned;

more inner-syntax markup;

tuned proofs;

more ambitious rendering: highlight active area for mouse hovering without modifier;

tuned proofs;

show_consts_markup is enabled by default;

clarified signature (again, reverting ec1023a5c54c);

clarified signature: more explicit Syntax.print_mode_tabs, depending on print_mode_value (); tuned data structures;

redundant;

tuned signature;

performance tuning: cache markup and extern operations;

minor performance tuning;

minor performance tuning;

backout somewhat pointless 5ea48342e0ae: no need to declare syntax consts for translations (e.g. constraints);

tuned;

tuned;

revert redundant guard (T = dummyT) from 0278f6d87bad;