New rule: unicode-bom

[feross]

http://eslint.org/docs/rules/unicode-bom

This was previously covered by no-irregular-whitespace but BOM characters at the beginning of files are now stripped by eslint, so adding this rule just gets us the old behavior again.

[dougwilson]

What is the suggested value for the rule? "never" I assume?

[feross]

Yep. Setting it to "never" would match the old behavior of the no-irregular-whitespace rule.

[yoshuawuyts]

I'm only like half-understanding this rule; not spotting any way it affects anything I've ever done with JS so 👍 I guess

[feross]

@yoshuawuyts See #283 for some more context, if you're interested.

[feross]

This rule will be included in standard v8