Harold

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+ Requirement of NumPy is changed to 1.13 and above. Among others, we need
`__array_ufunc__` override mechanism for representation algebra. This
should not be an issue since noone seems to use this.
+ The representations can now be sliced with `G[:,1:3]` etc.

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+ Sanitized the circular dependencies a bit more
+ minimal_realization is changed to accept models instead of A,B,C triplet
+ minimal_realization for Transfer uses the pole zero cancellation check
+ more housekeeping and bug fixes
+ added damping, natural frequency properties of poles
+ state_to_transfer does not return minimal realizations (per request)

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+ More tests
+ bode, nyquist plots with matplotlib
+ Rewritten the transmission_zeros to improve accuracy
+ Removed the single file and replaced it with modular files.
+ Refactored Riccati solvers to SciPy official repo
+ Lyapunov solver safety net is moot. Created PR 6775 in SciPy

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+ Added Riccati solvers
+ More documentation
+ Added safety net for lyapunov solvers in case there is no solution

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+ Added Lyapunov solvers
+ Fixed many bugs
+ Removed block diag and switched to scipy version

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+ Initial versioning and packaging.
+ Adding documentation and Sphinx integration.
+ Basically everything there is.