Add unsteady capabilities

[taylormcd]

This adds unsteady analysis capabilities and additional tests.

It also officially changes the package name to VortexLattice.jl. This will break existing links until the repository name is changed.

[juddmehr]

Not sure how to view all the compiled docs and stuff, so I read the current stuff and then skimmed the commits for this pull request and here are my feedback for those: Docs:

Overall:

• Why is the repo called VLM.jl but the package called VortexLattice? Can’t the repo name be changed easily?

Getting Started:

• It’s not really clear why you use sine spacing on a half wing to get cosine spacing on the full thing. When I run both myself, I can see that it works, but it seems more of a direction thing than an implementation thing. Is the sine spacing actually different, or is it just cosine spacing started at the opposite end of the wing?
• It seems like the discretization scheme should be able to be defined by a custom function. If that’s true, it might be worth mentioning in the docs.
• Overall, I think this is just the right scope for a getting started tutorial.

Examples:

• if there’s a way to turn on line wrapping, that might be nice. some of the code extends beyond the right edge of the code window, requiring horizontal scrolling to see.
• I think there should be more examples. Everything is symmetric in these examples. What about a non-symmetric example, or something a bit more complicated in the geometry.
• If it can be done as-is with just geometry inputs, it might be nice to have an example with control surfaces.
• Is there an example (or 2) for the new unsteady stuff?

Library:

• how does the metadata dictionary work with the write_vtk function?
• I would like some more info on how the paraview files are organized. It would be nice to be able to color the wing surface and the vortices different colors for starters, so I can see where the actual geometry starts/ends.
• It might be nice to tell about how the additional_velocity ruction is called within the Freestream function. What are the r’s that are going to be input? In what frame are they?
• Overall, things look good.