v0.6.0

• new solvers:
  • ToySolver.SAT.SLS.ProbSAT and sample probsat program
• new converters:
  • ToySolver.Converter.NAESAT
  • ToySolver.Converter.SAT2MaxCut
  • ToySolver.Converter.SAT2MaxSAT: SAT and 3-SAT to Max-2-SAT converter
  • ToySolver.Converter.QBF2IPC
  • ToySolver.Converter.QUBO: QUBO↔IsingModel converter
• new file format API:
  • merge ToySolver.Text.MaxSAT, ToySolver.Text.GCNF, ToySolver.Text.QDimacs, and ToySolver.Text.CNF
    info ToySolver.FileFormat and ToySolver.FileFormat.CNF
  • allow reading/writing gzipped CNF/WCNF/GCNF/QDimacs/LP/MPS files
• rename modules:
  • ToySolver.Arith.Simplex2 to ToySolver.Arith.Simplex
  • ToySolver.Arith.MIPSolver2 to ToySolver.Arith.MIP
  • ToySolver.Data.Var to ToySolver.Data.IntVar
• ToySolver.SAT:
  • add cancel function for interruption
  • introduce PackedClause type
• ToySolver.Arith.Simplex
  • introduce Config data type
  • implement bound tightening
• switch from System.Console.GetOpt to optparse-applicative
• stop supporting GHC-7.8