feature: ESM version exports deepMerge function

`deepMerge` function used by the package for deep merging multiple objects is now exported.

src/Collapsable.ts

@@ -1,5 +1,5 @@
 import { CollapsableItem } from './CollapsableItem'
-import { DeepPartial, mergeDeep } from './utils'
+import { DeepPartial, deepMerge } from './utils'
 import { CollapsableExtLink } from './CollapsableExtLink'
 
 export type CollapsableOptions = {
@@ -76,7 +76,7 @@ export class Collapsable {
 	}
 
 	public constructor(elements: HTMLElement | NodeListOf<HTMLElement>, options?: DeepPartial<CollapsableOptions>) {
-		this.options = mergeDeep({}, this.defaults, options) as CollapsableOptions
+		this.options = deepMerge({}, this.defaults, options) as CollapsableOptions
 		this.promiseOpen = false
 
 		if (elements instanceof NodeList) {

src/index.esm.ts

@@ -1,3 +1,2 @@
-import { Collapsable } from './Collapsable'
-
-export default Collapsable
+export { deepMerge } from './utils'
+export { Collapsable as default } from './Collapsable'

src/index.ts

@@ -1,3 +1 @@
-import { Collapsable } from './Collapsable'
-
-export default Collapsable
+export { Collapsable as default } from './Collapsable'

src/utils.ts

@@ -6,22 +6,22 @@ function isObject(item: unknown) {
 	return item && typeof item === 'object' && !Array.isArray(item)
 }
 
-export function mergeDeep(target: any, ...sources: any): Record<string, unknown> {
+export function deepMerge(target: any, ...sources: any): Record<string, unknown> {
 	if (!sources.length) return target
 	const source = sources.shift()
 
 	if (isObject(target) && isObject(source)) {
 		for (const key in source) {
 			if (isObject(source[key])) {
 				if (!target[key]) Object.assign(target, { [key]: {} })
-				mergeDeep(target[key], source[key])
+				deepMerge(target[key], source[key])
 			} else {
 				Object.assign(target, { [key]: source[key] })
 			}
 		}
 	}
 
-	return mergeDeep(target, ...sources)
+	return deepMerge(target, ...sources)
 }
 
 // UID for CollapsableItem