Describe the bug

It seems like the definition for BSkeletonImg (and the other BSkeleton helpers) is not exported

Steps to reproduce the bug

In a SFC

import { BSkeletonImg } from 'bootstrap-vue'

export default {
  name: 'MyComponent',
  components: {
    'b-skeleton-img': BSkeletonImg
  }
  ...
}

Compiler will complain with

"export 'BSkeletonImg' was not found in 'bootstrap-vue'

and the component will not be rendered

Expected behavior

It should be possible to import the helpers.

Versions

Libraries:

• BootstrapVue: 2.17.1
• Bootstrap: 4.5.2
• Vue: 2.6.12

Environment:

All environments

Demo link

Must be done in a webpack environment, can not provide demo link

Additional context

Add the missing exports here:

https://github.com/bootstrap-vue/bootstrap-vue/blob/dev/src/index.js#L288