gitignore
safe API for type inference, using the error monad everywhere (also in Util_tptp)
simplify interface for De Bruijn in ScopedTerm;
more compact implementation using iterators
updated quick tests
update tests (so that "make test" runs all tests including quick ones)
changed printing of arith variables
update .merlin file
new module, Sourced, for remembering where formulas/terms come from;
removed corresponding ugly tuples in FOTerm, HOTerm and Formula
merge from dev