Adding flat_params function

[pebeto]

This PR solves the requested by @ablaom in #176. The previous implementation has been simplified by the use of the holy traits pattern.

[ablaom]

Thanks for this @pebeto .

I don't understand why you now return a dictionary, where previously we returned a named tuple (which is what the doc-string example returns). Is there a good reason for returning a dictionary? (Incidentally, you can also merge named tuples). Dictionaries have the disadvantage of losing the information about the order of the properties, which could be inconvenient, don't you think?

[codecov-commenter]

Codecov Report

Merging #177 (9cc45b8) into dev (60ea476) will increase coverage by 0.23%.
The diff coverage is 100.00%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@            Coverage Diff             @@
##              dev     #177      +/-   ##
==========================================
+ Coverage   88.97%   89.21%   +0.23%     
==========================================
  Files           8        8              
  Lines         372      380       +8     
==========================================
+ Hits          331      339       +8     
  Misses         41       41              

Files Changed	Coverage Δ
src/parameter_inspection.jl	100.00% <100.00%> (ø)

[ablaom]

Looks good to me.