Add clean makefile target.
Add file encoding declarations.
Minor cleanup.
Use namedtuple for settings.
Do not error if path is missing and validation disabled.

Fixes #57.
Add settings documentation.
Break out getting exclude paths into own function.
Minor reformatting.
Clarify documentation.
Merge pull request #59 from wting/wting_57_add_path_validation_toggle

Add path validation setting.