'use strict' in all of the files

Moving conversation from #341.

I am not against using 'use strict', but if we do so, I’d like to consider switching to using strict-standard instead of standard. Or possibly eslint + eslint-config-standard + some strict config (the reasoning being that it’s more likely that a given editor will have eslint support available more readily than standard - this may just mean that we keep some form of standard for npm test, and just add an .eslintrc to the project).

See also:

• https://github.com/feross/standard/issues/382

[feross]

Ahh, you can also just add eslint-config-standard as a dependency to package.json, and add an .eslintrc:

{
  "extends": "standard"
}

[develar]

The rest we should disable.

The problem that we cannot customize rules. As @feross suggested, in my upcoming PR I use eslint-config-standard.