chore: add and import types

Author: selemondev

src/index.ts

@@ -1,2 +1,2 @@
 export { default as VueSignaturePad } from './components/VueSignaturePad.vue'
-export type { CanvasOptions, Props, WaterMarkObj } from './types'
+export type { CanvasOptions, Props, WaterMarkObj, SignatureRef, CanvasSignatureRef } from './types'

src/types/index.ts

@@ -31,6 +31,11 @@ export interface SignatureRef {
   penColor?: string
 }
 
+export interface CanvasSignatureRef {
+  isCanvasEmpty?: () => void
+  saveSignature?: (format?: string) => void
+}
+
 export interface Props {
   options: Options
   width: string