todo
todo
move 2d/3d column selection to Run level
caching: pickle -> numpy

move to a native numpy format for caching run data.

important? difference is that now only the data arrays (x, z, u, w, t)
of a run are saved, rather than the whole run object.
doc
tidy, remove excessive save.
state when cache loaded
path spec should be in bashrc, not here
reynolds decomposition
todo
plot momentum flux
quiver overlay
todo