Plotting graph of equations for FramedAgentType

[sbenthall]

This PR introduces into FramedAgentType the mechanics for frames to reference each other as 'parents' and 'children', including 'back' and 'forward' references when these frames are in a different period.

This enables the plotting of a MACID style network diagram representing the problem, as in the following case (taken from the example notebook):

• Tests for new functionality/models or Tests to reproduce the bug-fix in code.
• Updated documentation of features that add new functionality.
• Update CHANGELOG.md with major/minor changes.

[sbenthall]

This builds on #1064, which should be merged first.

[codecov-commenter]

Codecov Report

Merging #1071 (c6b7dd0) into master (a5634ab) will increase coverage by 0.04%.
The diff coverage is 89.55%.

@@            Coverage Diff             @@
##           master    #1071      +/-   ##
==========================================
+ Coverage   73.60%   73.64%   +0.04%     
==========================================
  Files          69       69              
  Lines       10519    10576      +57     
==========================================
+ Hits         7742     7789      +47     
- Misses       2777     2787      +10     

Impacted Files	Coverage Δ
HARK/frame.py	92.42% <84.78%> (-4.09%)	⬇️
HARK/ConsumptionSaving/ConsPortfolioFrameModel.py	95.23% <100.00%> (-4.77%)	⬇️
...mptionSaving/tests/test_ConsPortfolioFrameModel.py	100.00% <100.00%> (ø)

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[alanlujan91]

This looks good to me. Is there a way to provide a pseudo-simulation history of shocks that can be used by both agent types? In this way, they both experience the same exact shocks, and differences would be fully attributable to bugs and not to changes in random draws.

[sbenthall]

That's an excellent idea.

I believe there is support for this in the library, but I've never used it:

HARK/HARK/core.py

Lines 553 to 556 in a5634ab

	if self.read_shocks: # If shock histories have been pre-specified, use those
	self.read_shocks_from_history()
	else: # Otherwise, draw shocks as usual according to subclass-specific method
	self.get_shocks()

Let me try that out before merging. Thanks for the review!

[sbenthall]

Ok, I tried copying the shock history over from the first portfolio simulation to the Framed version and using read_shocks.

The results were somewhat unexpected:

• The shock values did not line up exactly.
• But the results of the simulation (i.e, derived values, such as mNrm) did come into closer alignment.

I may well be using read_shock incorrectly and so this needs more investigation.

But since that testing is somewhat orthogonal to the plotting work here, I'll merge this PR and address this in a different issue.