Process Costing Framework Documentation

[bpaul4]

Fixes

Summary/Motivation:

Changes proposed in this PR:

• Updated documentation for Process Costing Framework (name is not finalized)
• Replaces existing documentation for the unit_costing() methods at https://github.com/IDAES/idaes-pse/blob/main/docs/reference_guides/core/util/unit_costing.rst, which is left alone for now but could be removed as part of this update
• A new example for this framework is added in https://github.com/IDAES/examples-pse/pull/124

Legal Acknowledgement

By contributing to this software project, I agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the license terms described in the LICENSE.txt file at the top level of this directory.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov[bot]]

Codecov Report

Merging #928 (a66f84a) into main (2e77676) will decrease coverage by 0.00%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #928      +/-   ##
==========================================
- Coverage   70.32%   70.32%   -0.01%     
==========================================
  Files         576      576              
  Lines       64619    64619              
  Branches    12138    12138              
==========================================
- Hits        45446    45443       -3     
- Misses      16872    16876       +4     
+ Partials     2301     2300       -1     

Impacted Files	Coverage Δ
idaes/models/costing/SSLW.py	83.43% <100.00%> (ø)
idaes/ver.py	61.53% <0.00%> (-4.62%)	:arrow_down:

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[andrewlee94]

@MAZamarripa could you suggest someone else to review this (unless you intend to do it yourself)?