osl_func utility: run any function from the command line

[matsvanes]

This is a utility function addition to run any osl function (with limitations) from the terminal command line, i.e., osl_func function_name arg1 arg2.
Example:
osl_func osl.source_recon.rhino.polhemus.delete_headshape_points None None polhemus_headshape.txt will iteratively load the (sub-) module until it reaches the function, and then run the function with the function arguments. This example will run osl.source_recon.rhino.polhemus.delete_headshape_points(recon_dir=None, subject=None, polhemus_headshape_file='polhemus_headshape.txt').

This is especially useful for interactive functions, which often don't work very well in Jupyter Notebook. Because I expect that this is an issue that many people will face, I thought this would be useful (so users don't have to make separate scripts for this purpose every time). The main limitation currently is that you can only use functions with string, boolean, or None arguments.