BCD adder

BCD adder tests

BCD adder

removed some errors

removed some errors

Removed errors according to carry,sum

Update combinational.py

pep8

some changes according to PEP8

Update combinational.py

Final PEP8 fix
Merge pull request #177 from sarwarc/develop

Added BCD adder and tests
Add AUTHORS file

This reverts commit fa5a89b6b45151ff9fdf8a4cfe1d1a6e069dd384.
Merge pull request #184 from debugger22/AUTHORS

Add Authors file
Add tests to check support for python 2.6 and 3.2 as well