feat: add custom prop types to propTypes object (#39)

* feat: add custom prop types to propTypes object

* fix: export named function too

src/index.js

@@ -1,3 +1,18 @@
-export { arrayWithLength } from './arrayWithLength'
-export { instanceOfComponent } from './instanceOfComponent'
-export { mutuallyExclusive } from './mutuallyExclusive'
+import propTypes from 'prop-types'
+
+import { arrayWithLength } from './arrayWithLength.js'
+import { instanceOfComponent } from './instanceOfComponent.js'
+import { mutuallyExclusive } from './mutuallyExclusive.js'
+
+const customPropTypes = {
+    arrayWithLength,
+    instanceOfComponent,
+    mutuallyExclusive,
+}
+
+export { arrayWithLength, instanceOfComponent, mutuallyExclusive }
+
+export default {
+    ...propTypes,
+    ...customPropTypes,
+}