Polish + Prepare IEEEST for release

[lukelowry]

Description

Added doxygen and made one functional correction to the model (initialization).

Proposed changes

• Doxygen comments for model and enums
• Initialization fixed to work on signals that are not zero-valued at steady state
• Implicit representation resolves any parameter problems for the purpose of validation until we merge IEEEST Stabilizer Improvements/Corrections #460

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• N/A I have updated CHANGELOG.md to reflect the changes in this PR. If this is a minor PR that is part of a larger fix already included in the file, state so.

Further comments

Half of the model is already implicit, so this jsut make it consistent and helps with the ugly parameter validation until a cleaner design is approved.

[pelesh]

I think we need to consider differential variable designation as the compile-time requirement, because it will become so once we introduce Hessenberg form for DAEs.

[pelesh]

I believe we agree that this cannot be the way to configure differential and algebraic variables. This approach will work with implicit DAE formulation but will fail for Hessenberg form.

If we are to pack models of different order in this component, we do need to add separate residual functions for each order. I don't see way around it.

[lukelowry]

I agree. I think that the template parameter approach (the other PR) is the cleanest. Think starting with this which shows all the permutations is a good starting point showing the requirements so we can design the compile time version maintainably

[pelesh]

Closing in favor of #460