File created, not functional.

the file, linear_regression.py, is updated and includes some error
handling. For some reason, the code is not iterating properly. Each
time the code is run, the plot that is generated includes the previous
groups. I am not sure why this is happening.

I think I have the file so it should now work if no group is supplied.
I also added a few more comments to the code.

I just tested the code with group turn off for iris.csv and it worked.
I had to made a few changes, but I think the code is functional, though
I want to polish it up a bit more. I think I will include this in my
final project, so I need to figure out how to integrate it.

The issue that was causeing other graphs in the for loop to contain
the data from the previous iteration was solved by clearing the plot at
the end of each iteration.