Additional features for Section.display_results()

[jwprusi]

I've got a couple of proposals, and I've elected to split them between two discussions because they can be discussed and implemented separately. This is the first of two discussions.

I'd propose the addition of two additional features for Section.display_results(). I've implemented both of these for my own personal use by subclassing Section and creating my own display_results function, which is probably not a good idea for long-term use, but I didn't want to do a more elaborate implementation unless there's interest from others.

1. Ability to directly output to a file within the function. When I've used this package, it's been primarily to feed further analyses, and having an output file that can be stored with other computations as an appendix is useful. Assuming there's not an easy "Pythonic" way to pass the output table to a file that I'm missing (possible, I'm an indifferent programmer), I'd propose adding a new argument file= to Section.display_results() and post.print_results(). The end of post.print_results(file=f) can use the rich.print() function, which takes a file argument to print to file:

    if file is not None:
        rich.print(table, file=file)

This will enable this to be consistent with the print() function to create titles and headers when using the package:

with open(filename, 'w', encoding='utf-8') as f:
    print(front_matter_str, file=f) # Printing front matter to the file explaining what was computed
    section.display_results(file=f) # Proposed new usage to place results in file

2. The ability to add a column explaining the nomenclature. I find that the amount of data output makes it easy to lose track of precisely what each output item means, so having another column in the table that explains each item is helpful when reviewing results months to years later.

My solution iterates over a dict made from the SectionProperties comment block, and directly reads SectionProperties.<property>, rather than using the Section.get_<property>() functions like post.print_results() does so it needs a lot of work before it's ready for a PR, but the results that I propose look like this:

┏━━━━━━━━━━━┳━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Property  ┃         Value ┃ Explanation                                 ┃
┡━━━━━━━━━━━╇━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┩
│ area      │  3.100790e+00 │ Cross-sectional area                        │
│ perimeter │  1.862900e+01 │ Cross-sectional perimeter                   │
│ qx        │ -3.504141e-15 │ First moment of area about the x-axis       │
│ qy        │  1.538588e+00 │ First moment of area about the y-axis       │
│ ixx_g     │  1.524298e+01 │ Second moment of area about the global      │
│           │               │ x-axis                                      │
│ iyy_g     │  1.612224e+00 │ Second moment of area about the global      │
│           │               │ y-axis                                      │
│ ixy_g     │ -2.829822e-15 │ Second moment of area about the global      │
│           │               │ xy-axis                                     │
│ cx        │  4.961921e-01 │ X coordinate of the elastic centroid        │
│ cy        │ -1.130080e-15 │ Y coordinate of the elastic centroid        │

Do these seem useful to others and worth further development?