Need to enhance a solver-level message reporting facility, maybe with a verbosity selection

[yungyuc]

Originally reported by: Yung-Yu Chen (BitBucket: yungyuc, GitHub: yungyuc)

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Currently solvcon.solver.MeshSolver.mesg() is the only and primitive message reporting facility available at the solver level. Also, there's no verbosity control.

The case-level message reporting (solvcon.case.MeshCase.out()) doesn't have verbosity control either. Verbosity control should be taken into consideration for both reporting levels.

The verbosity may use 5 or 7 levels. The lack of verbosity and the crippled solver-level reporting hinder code debugging a lot.

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• Bitbucket: https://bitbucket.org/solvcon/solvcon/issue/102