Add beforeDraw and afterDraw hooks to the annotations

[stockiNail]

This PR is adding before/after draw hooks in order to allow the user to apply whatever needed customization on out-of the-box annotations. Fix #146.

The hooks will be invoked once for every annotation for each drawing cycle.

plugins: {
  annotation: {
    annotations: {
      line: {
        type: 'line',
        ....
        beforeDraw(context) {
          console.log('beforeDraw');
        },
        afterDraw(context) {
          console.log('afterDraw');
        },
      },
    }
  }
}

Hook	Arguments	Return type	Default	Description
beforeDraw	context	void	annotation.beforeDraw	invoked before the element drawing
afterDraw	context	void	annotation.afterDraw	invoked after the element drawing

Common hooks for all annotations can be set in the annotation plugin options:

plugins: {
  annotation: {
    beforeDraw(context) {
      console.log('Common beforeDraw');
    },
    afterDraw(context) {
      console.log('Common afterDraw');
    },
    annotations: {
      line: {
        type: 'line',
        ....
      },
    }
  }
}

TODO

• test cases
• types
• documentation
• samples

[kurkle]

I still don't like the counters
How about making it simpler, just draw before/after the main element is drawn?
We could add afterDrawChildren later, if it's really needed.

[stockiNail]

I still don't like the counters
How about making it simpler, just draw before/after the main element is drawn?
We could add afterDrawChildren later, if it's really needed.

I think its reasonable
But Let me take time to review the PR
My memory is not so persistent and I dont remember so well what I wrote

[stockiNail]

How about making it simpler, just draw before/after the main element is drawn?

done! review applied!

No counters anymore!

[kurkle]

Sorry for the huge delay on these. LGTM