Liquepy

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* Added calculation of dissipated energy and cumulative absolute change in shear stress of element tests

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* Added plotting functions for CPT
* Cleaned up names of input motion saving functions, and order of args

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* Updated docstrings, readme file
* Fixed number of columns to load on CPT to be 0-3

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* `run_bi2014` fixed bug where water unit weight was 10 times too big

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* `BoulangerIdriss2014` unit weight calculation now uses the specific weight of water a gravity=9.8
* `BoulangerIdriss2014` gwl now is the ground water level during the earthquake, while cpt_gwl is the gwl at cpt measure
* Added `BoulangerIdriss2014CPT` which performs `BoulangerIdriss2014` but takes CPT as an input

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* Changes to `BoulangerIdriss2014`:
* Added `big_q` as a property
* Modified unit weight calculation (minimum changed from 15kN/m3 to 14.715kN/m3 (lowest value in original study
by Roberston (2010)), Added maximum unit weight 19.62kN/m3 (maximum value in study),
* Changed atmospheric pressure from 100kPa to 101kPa (also added as an optional input)
* Input `magnitude` -> `m_w`
* Added support for calculation of unit weight using specific weight
* Optional input `s_g` to override specific weight of 2.65
* Optional input `s_g_water` to override specific weight of water