SubDyn summary file: fixes

[RBergua]

I believe this pull request can be merged.

Feature or improvement description
SubDyn can output in the summary file (SumPrint = 1) the cosine matrices (OutCOSM = True).

In the summary file, the direction cosine for a spring element is not properly written. The summary file looks as:

As can be observed, the summary file shows only zeros for the spring element. This is because the subroutine OutSummary tries to get the direction cosine based on the joint 1 and joint 2 of the member (and joint 1 and joint 2 are coincident for springs). In this PR, the subroutine OutSummary has been modified to properly account for the spring element (and arbitrary beams in the future).

However, I believe that if the user defines a given direction cosine for a circular beam, the subroutine GetDirCos will also compute the direction cosine based on joint 1 and joint 2, effectively overwriting whatever the user provided as input.

Impacted areas of the software
SubDyn summary file.

Test results, if applicable
Proper summary file:

[andrew-platt]

Could you change out the tab characters for spaces? Otherwise I approve

[andrew-platt]

For @andrew-platt:

• Check that readthedocs renders when this PR is merged (updates to webhook might have broken the intergration)