write Field II mesh interpolation function

[mlp6]

instead of having to always re-run Field II when using a new mesh, we should have a function that will take an existing 3D Field II intensity output and 3D map it onto a new grid

[mlp6]

http://docs.scipy.org/doc/scipy-0.14.0/reference/generated/scipy.interpolate.griddata.html

[mlp6]

This seems to be more important of a feature now for a few reasons:

1. Field II doesn't play nicely with RAM and meshes that have large absolute extents (regardless of mesh density), which reared its head when trying to simulate the 4V1c
2. field2dyna doesn't need to chug through tons of points when doing a shear wave simulation and the vast majority of the nodes are outside the footprint of the active array aperture
3. Migrating to the C-version of Field II Pro would be easier to just specify a 3D array of points in the source code than to have to read in the nodes.dyn file.

[mlp6]

@mjr52 your task to integrate the HFR-ARFI beams in falls under this Issue. Would be nice to make something that works for both applications (HFR-ARFI and the use-case detailed above).

[mlp6]

@jrichardson97 your branch that I'm merging in (#121) does this now, correct?

[jrichardson97]

Yes. I'll make an example with a sample load file and the interpolation constraints

[mlp6]

@jrichardson97 you will need to create a new branch off of main for that as I just merged in your large pull request after some tweaks to the testing environment. I'll let you close this Issue when that PR is ready to go.