1075/enhancement/Make col class with __getattr__

[deanm0000]

Which issue does this PR close?

Closes #1075

Rationale for this change

To improve ergonomics of the API by providing a quicker way of accessing columns using the __getattr__ method of classes. Using the __call__ method, the original behavior is maintained, this is only additive.
Now this is possible

from datafusion import col as c

my_a_column=c.a
my_banana_column=c.banana

What changes are included in this PR?

A new col.py file with the class. I removed the col and column function from __init__ and imported col and column from col.py. I added a test that duplicates another test but uses the new syntax.

Are there any user-facing changes?

Only optional ones as mentioned above.

No breaking changes.