add academic fea example

[akaszynski]

Convert academic example from internal examples to public example. Minor modifications to use ansys-mapdl-core==0.51.8, but otherwise example kept intact.

Pinging @jazztekk for visibility and credit. Thanks for your work!

[germa89]

Great example.

I just did some minors modifications in a push. Now we use to_array method.

[germa89]

Great example @jazztekk

[germa89]

Btw, I also implemented an improvement on the .to_list method.

I believe it should help towards #828.

[akaszynski]

Failing due to:

PRINT F    REACTION SOLUTIONS PER NODE
       1   0.1287512532E+008  0.4266737217E+007
       2  -0.1512012179E+007  0.2247558576E+007
       3  -0.7065315064E+007 -0.4038004530E+007
       4  -0.4297798077E+007 -0.2476291263E+007