New version: NeumannKelvin v0.8.0

[JuliaRegistrator]

• Registering package: NeumannKelvin
• Repository: https://github.com/weymouth/NeumannKelvin.jl
• Created by: @weymouth
• Version: v0.8.0
• Commit: 410fc9c291c20f9873c3ba0e1e1f02bb562e8020
• Reviewed by: @weymouth
• Reference: weymouth/NeumannKelvin.jl@410fc9c#commitcomment-175325545
• Description: Linear free surface potential flow using Neumann-Kelvin Greens Functions.
• Release notes:

v0.7.0

# Breaking changes
New workflow! First you create a specific PanelSystem (Body, FS, or NK) based on panels and other arguments. Then you run a solver (direct or gmres) and then measure it (Φ, ∇Φ, u, cₚ, steadyforce, addedmass). All of the information is kept within the struct (like Froude length, mirrors, etc) so you are sure to be solving and then measuring the same system. 

# New features
- Free surface source panels system. Applies the linear FSBC on source panels instead of the Neumann-Kelvin condition on body panels. The convective derivative is applied using an upwinded finite-difference stencil, so the freesurface panels must be organized in a structured grid.
- PanelTree struct. Organizes a table of panels into a tree using ImplicitBVH.jl and specializes Φ to use an accelerated O(log(N)) summation over that tree, using aggregated monopole versions of the panels if far enough away. This can't be applied to the Neumann-Kelvin potential, but it's great for very large sets of source panels. 
- GMRES solver. Approximate iterative matrix-free solution of the panel system. This is extremely memory efficient and very fast when coupled with a PanelTree. Includes a simple downwind residual flooding preconditioner for FSPanelSystems. Still takes O(100) iterations for those systems. 
- GeometryBasics extension for STLs. Mesh objects can be panelized to create a table of panels. The exact planar ∫G function is applied to these panels. 

# Other improvements
- Zero allocation green's function and Φ, ∇Φ methods!
- Much better viz functionality for both backends. New default plots for the PanelSystem types.

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