fix(ts): export FuseIndex type

Export FuseIndex type in the namespace. Fixes #519

Author: krisk

src/index.d.ts

@@ -5,7 +5,7 @@ declare class Fuse<T> {
   constructor(
     list: ReadonlyArray<T>,
     options?: Fuse.IFuseOptions<T>,
-    index?: FuseIndex<T>
+    index?: Fuse.FuseIndex<T>
   )
   /**
    * Search function for the Fuse instance.
@@ -25,12 +25,12 @@ declare class Fuse<T> {
    * @param options `Fuse.FuseSearchOptions`
    * @returns An array of search results
    */
-  search<R = T>(
+  search<T>(
     pattern: string | Fuse.Expression,
     options?: Fuse.FuseSearchOptions
-  ): Fuse.FuseResult<R>[]
+  ): Fuse.FuseResult<T>[]
 
-  setCollection(docs: ReadonlyArray<T>, index?: FuseIndex<T>): void
+  setCollection(docs: ReadonlyArray<T>, index?: Fuse.FuseIndex<T>): void
 
   /**
    * Adds a doc to the end the list.
@@ -52,7 +52,7 @@ declare class Fuse<T> {
   /**
    * Returns the generated Fuse index
    */
-  getIndex(): FuseIndex<T>
+  getIndex(): Fuse.FuseIndex<T>
 
   /**
    * Return the current version.
@@ -89,28 +89,28 @@ declare class Fuse<T> {
     keys: Array<Fuse.FuseOptionKey>,
     list: ReadonlyArray<U>,
     options?: Fuse.FuseIndexOptions<U>
-  ): FuseIndex<U>
+  ): Fuse.FuseIndex<U>
 
   static parseIndex<U>(
     index: any,
     options?: Fuse.FuseIndexOptions<U>
-  ): FuseIndex<U>
+  ): Fuse.FuseIndex<U>
 }
 
-declare class FuseIndex<T> {
-  constructor(options?: Fuse.FuseIndexOptions<T>)
-  setSources(docs: ReadonlyArray<T>): void
-  setKeys(keys: ReadonlyArray<string>): void
-  setIndexRecords(records: Fuse.FuseIndexRecords): void
-  create(): void
-  add(doc: T): void
-  toJSON(): {
-    keys: ReadonlyArray<string>
-    collection: Fuse.FuseIndexRecords
+declare namespace Fuse {
+  export class FuseIndex<T> {
+    constructor(options?: FuseIndexOptions<T>)
+    setSources(docs: ReadonlyArray<T>): void
+    setKeys(keys: ReadonlyArray<string>): void
+    setIndexRecords(records: FuseIndexRecords): void
+    create(): void
+    add(doc: T): void
+    toJSON(): {
+      keys: ReadonlyArray<string>
+      collection: FuseIndexRecords
+    }
   }
-}
 
-declare namespace Fuse {
   type FuseGetFunction<T> = (
     obj: T,
     path: string | string[]