Multiple definitions of BOUNDSPEC for more than one side/segment

[pbranson]

BOUNDSPEC can be used multiple times in a swan input file to define the boundary condition on the given side. Similarly for segments, each segment could have a separate BOUNDSPEC line with input sp2 or TPAR.

This PR has a first example of how to enable the use of the SIDES object, but should be generalised for segments too - TBD

Rasing the PR now and will add additional mods later for segment. Seeking feedback @rafa-guedes

[rafa-guedes]

This makes sense @pbranson. I normally use boundnest1 rather than boundspec to prescribe the boundary in swan so I'm not entirely familiar with the different ways you could use it such as what you describe here. I think your approach looks good, perhaps if you could add some example in the tests to see how this will render, that would be helpful. Otherwise I'm happy for you to go ahead with the idea.