Introduce double negation in rule bodies.
Parse choice rules.
Fix bug with tautological clauses added by completion in presense of choice rules.
Add assert in addClause() to check that no tautology is added to the clause set.
Fix simplifications for choice rules.
Add test cases in gringo 3 notation.
Minor fix.
Fix bug with double negated literals in GUS structures (but a more indepth revision is required).
Implemented aggregates as PostPropagators.
Added missing file and some tests.
Merge branch 'choice' into aggregates

Conflicts:
	src/input/GringoNumericFormat.cpp
	src/input/GringoNumericFormat.h
Removed useless prints.
Fixed bug when satelite infers literals that are in propagators.
Added test cases
More tests.
Optimization of memory usage.
Satelite data structures are not created if the number of clauses is greater than one million.
Remove lastSwapIndex.
Fix warning on unsigned and signed comparison.
Put activity and signature of Clause in a union.
Learned clauses must use addLiteralInLearnedClause instead of addLiteral.
Remove variable signature in Variable (we compute it online).
Bufferize stdin.
Use unsigned instead of int for sizes to improve parsing performance.