DEV: Revised and added basic image math operations for merge

The implementation that I tried originally did not work due to issues
with wrapping docstrings from numpy. I originally tried importing any
and all functions that are already available in numpy directly through
the API interface, however, param types such as "numpy array" do not
conform to our standard types.
After that I tried to simply reassign the function documentation, but
ran into errors doing that as well, though I will be able to figure that
out after AGU.
SO: Some restructuring remains to be completed but all functionality
works as expected in the current implementation.
DEV: renamed avizo and netCDF file loader funcs with prefix read_

The functions were previously named load_netCDF and load_amiramesh
Now the functions are named:
    read_netCDF
    read_amiraMesh
DEV: Finished adding basic tomo image processing tools req. for seg

THis commit also includes a file-IO tool set that properly (and
ACTUALLY) works well with 3D tiff files. The tool set includes both a
reader and a writer.