Andes

This version accelerates computations by about 35%.

- Models with flag ``collate=False``, which is the new default,
will slice DAE arrays for all internal vars to reduce copying back and forth.
- The change above greatly reduced computation time.
For ``kundur_pss.xlsx``, simulation time is down from 2.50 sec to 1.64 sec.
- The side-effects include a change in variable ordering in output lst file.
It also eliminated the feasibility of evaluating model equations in
parallel, which has not been implemented and does not seem promising in Python.
- Separated symbolic processor and documentation generator from Model into
``SymProcessor`` and ``Documenter`` classes.
- ``andes prepare`` now shows progress in the console.
- Store exit code in ``System.exit_code`` and returns to system when called
from CLI.
- Refactored the solver interface.
- Patched Config.check for routines.
- SciPy Newton-Krylov power flow solver is no longer supported.
- Patched a bug in v0.9.0 related to `dae.Tf`.

This update contains a quick but significant fix to boost the simulation speed by avoiding
calls to empty user-defined numerical calls.

- In `Model.flags` and `Block.flags`, added `f_num`, `g_num` and `j_num` to indicate
if user-defined numerical calls exist.
- In `Model.f_update`, `Model.g_update` and `Model.j_update`, check the above flags
to avoid unnecessary calls to empty numeric functions.
- For the `kundur_pss.xlsx` case, simulation time was reduced from 3.5s to 2.7s.

- Changed `RefParam` to a service type called `BackRef`.
- Added `DeviceFinder`, a service type to find device idx when not provided.
`DeviceFinder` will also automatically add devices if not found.
- Added `OptionalSelect`, a service type to select optional parameters if provided
and select fallback ones otherwise.
- Added discrete types `Derivative`, `Delay`, and `Average`,
- Implemented full IEEEST stabilizer.
- Implemented COI for generator speed and angle measurement.

This release contains important documentation fixes and two new blocks.

- Fixed documentations in `andes doc` to address a misplacement of symbols and equations.
- Converted all blocks to the division-free formulation (with `dae.zf` renamed to `dae.Tf`).
- Fixed equation errors in the block documentation.
- Implemented two new blocks: Lag2ndOrd and LeadLag2ndOrd.
- Added a prototype for IEEEST stabilizer with some fixes needed.

- Converted the differential equations to the form of ``T \dot{x} = f(x, y)``, where T is supplied to
``t_const`` of ``State/ExtState``.
- Added the support for Config fields in documentation (in ``andes doc`` and on readthedocs).
- Added Config consistency checking.
- Converted `Model.idx` from a list to `DataParam`.
- Renamed the API of routines (summary, init, run, report).
- Automatically generated indices now start at 1 (i.e., "GENCLS_1" is the first GENCLS device).
- Added test cases for WECC system. The model with classical generators is verified against TSAT.
- Minor features: `andes -v 1` for debug output with levels and line numbers.

Version 0.6.9 is the last version for the numeric-only modeling framework.

This version will not be updated any more. But, models, routines and functions will be ported to the new version.