add file information to toml parse context and error messages;

add position information to toml parser and error messages;

properly concatenate toml files: regular toml rules still apply (e.g., inline values may not be changed), but values defined in one file may be updated in another;

allow re-defining keys in toml object (already checked during parse time);

clarified toString for toml objects;

tuned

tuned message;

better invalidation for schedule cache (only on relevant changes);

tuned;

timing heuristic: parallelize more aggressively to utilize hosts fully;