update warnings

Try to be smarter when it comes to mode-require-final-newline and
require-final-newline. In either case, just turn off
require-final-newline and work as expected, since the user has already
demonstrated by installing ethan-wspace and invoking the mode that they
want ethan-wspace to work correctly.
Add ethan-wspace-clean-all

This function immediately cleans all whitespace errors in the buffer and
enables ethan-wspace-clean-all-modes to make sure it stays clean.
Merge pull request #24 from expez/clean-all

Add ethan-wspace-clean-all-modes