Require newline at EOF

Newline at EOF is is a common convention that most tools expect. Not
having a newline at EOF is considered the exception. Examples include:

- Vim explicitly says '[noeol]' (default is to add newline).
- Git explicitly says 'No newline at at end of file'.
- Bash `read` fails to read the last line of the file.

Most importantly, it would be nice to have the same convention in all
files instead of them switching back and forth.