Include LICENSE.txt file in wheels

The license requires that all copies of the software include the license.  This makes sure the license is included in the wheels.  See the wheel documentation [here](https://wheel.readthedocs.io/en/stable/#including-the-license-in-the-generated-wheel-file) for more information.

Author: toddrme2178

setup.cfg

@@ -4,6 +4,9 @@ universal = 1
 [flake8]
 ignore = 'I201,I101,D100,D101,D102,D103,D200,D201,D202,D203,D204,D205,D211,D400,D401,D403,N802,N806,'
 
+[metadata]
+license_file = LICENSE.txt
+
 [isort]
 not_skip = __init__.py
 multi_line_output = 5