Enforce newline at end of files

[0xazure]

Trailing newlines are a common idiom in programming, and enabling this rule will save reviewers nitpicking or overlooking missing trailing newlines.

ESLint also supports the --fix option to automate fixing some of the problems reported by this rule.

There are no current files in the codebase that require fixing to add trailing newlines as verified by npm run lint.

[0xazure]

To consider:

This rule enforces at least one newline (or absence thereof) at the end of non-empty files.

If we want to enforce just one trailing newline, we would also need to enable no-multiple-empty-lines to control maxEOF.

[humphd]

I'll let @modeswitch review this one.