* Adds folder sensor
The state of the sensor is the time that the most recently modified
file in a folder was modified.
* Address lint errors
* Edit docstrings
Makes the recommended edits to docstrings
* Update .coveragerc
Add sensor/folder.py
* Update folder.py
* Address requests
Address requests changes
* Adds folder
* Adds test, tidy up
* Tidy
* Update test_folder.py
* Update folder.py
* Fix setup
Fix setup with else statement
* Update folder.py
* Update folder.py
* Remove list of files from attributes
* Update test_folder.py
* Update folder.py
* Update test_folder.py
* Update folder.py
* Update folder.py
Robin