warnings?

[shaunlebron]

maybe return warnings for the following things:

• parent-expression parent expression hack - notify when it will not work #148
• leading-close parens causing Paren Mode behavior allow plugins to indicate when indent-mode is diverted to paren-mode #136
• when parens are held by cursor https://github.com/shaunlebron/parinfer/issues/143#issuecomment-316125241