Reorganize solvcon.hook and solvcon.anchor modules and make solvcon.hook.MeshHook for MeshCase/MeshSolver.

[yungyuc]

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

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Make hook and anchor like the renewed case and solver.

Modules solvcon.case and solvcon.solver have been reorganized to define only the new solver system (entities that are based on solvcon.mesh.Mesh and Cython). Legacy code (that use ctypes) are put in *_legacy.py. Common code shared by the legacy system and the new system is in *_core.py.

solvcon.hook and solvcon.anchor should have the same structure.

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• Bitbucket: https://bitbucket.org/solvcon/solvcon/issue/59

[yungyuc]

Original comment by Yung-Yu Chen (BitBucket: yungyuc, GitHub: yungyuc):

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Fixes issue #59: reorganize hook and anchor modules.