Provide basic support for image manipulations.
The syntax is largely based on the IRAF task imarith:
``podi_imarith.py frame1.fits (op) frame2.fits output.fits
Note that instead of frame2.fits you can also specify a numeric value.
Operations currently supported are: * + addition * - subtraction * x multiplication * / division * ^ raise to the n-th power. This only works with numerical values as
second parameter.