separate (semi)ring with normalization

merged

more CONTRIBUTORS;

documentation for 'subgoal' command;

clarified module;

allow to specify suffix of goal parameters;

subgoal parameters are internal by default and named by user;

split multi-goals as usual (outermost Pure.conjunction only);

clarified prems: full subgoal is imported in any case, to avoid remaining schematic variables;

proper state after qed;

clarified keyword categories;

support for subgoal focus command;

tuned;

taylor series with has_integral and integrable_on

merged

no arguments for "standard" (or old "default") methods;

renamed "default" to "standard", to make semantically clear what it is;

tuned;

Merge

Useful lemmas. The theorem concerning swapping the variables in a double integral.

generalized inf and sup_continuous; added intro rules

fix tex-output for rel_mset

removed chained facts from preplaying -- and careful about extra chained facts when removing 'proof -' and 'qed' from one-line Isar proofs

clarified map_node: operate precisely on goal context and goal info (see also 2b8342b0d98c); apply_end cases are no longer seen in current context section (hardly relevant in practice);

improved scheduling for urgent tasks, using farm of replacement threads (may lead to factor 2 overloading, but CPUs are usually hyperthreaded);

clarified static phase; proper error;

tuned proofs;

more symbols;