Modified Cam Clay model: original nonlinear hypoelastic version

New

• original Modified Cam Clay (MCC) model with nonlinear hypoelasticity
• fully incremental (recommended) and absolute formulation added
• minimum value for the pre-consolidation pressure introduced
• => yield surface cannot degenerate to point anymore

Changes

• documentation re-written (focus on original hypoelastic model) (cf. Overleaf)
• new isotropic normal compression line (NCL) test for comparison

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2. Tests covering your feature were added?
3. Any new feature or behavior change was documented?