Decrease the numbers of warnings before 0.4.0!

• interp2d #27 (closed), see https://scipy.github.io/devdocs/notebooks/interp_transition_guide.html

• UserWarning: FigureCanvasAgg is non-interactive, and thus cannot be shown (from fluidimage/data_objects/display_pre.py:111, fluidimage/data_objects/display_piv.py:232)

• UserWarning: Possible precision loss converting image of type float64 to uint8 as required by rank filters. Convert manually using skimage.util.img_as_ubyte to silence this warning. (from fluidimage/preproc/io.py:62)

• RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (matplotlib.pyplot.figure) are retained until explicitly closed and may consume too much memory. (To control this warning, see the rcParam figure.max_open_warning). Consider using matplotlib.pyplot.close().

• MatplotlibDeprecationWarning: Getting the array from a PolyQuadMesh will return the full array in the future (uncompressed). To get this behavior now set the PolyQuadMesh with a 2D array .set_array(data2d). (from fluidimage/calibration/calib_direct.py:327, 334, 432, ...)