chore: export BiDirectionalDeepMap (#19)

Author: adamhamlin

index.ts

@@ -1,3 +1,4 @@
-export { DeepMap } from './src/map';
 export { DeepSet } from './src/set';
+export { DeepMap } from './src/map';
+export { BiDirectionalDeepMap } from './src/map.bi-directional';
 export { areEqual } from './src/areEqual';