Add wrapper code

.gitignore

@@ -5,3 +5,4 @@ index.node
 npm-debug.log*cargo.log
 cross.log
 cargo.log
+dist

index.node.d.ts

@@ -0,0 +1,8 @@
+/// An opaque type representing a native context.
+export type Context = unknown;
+
+export function new_ctx(): Context;
+export function db_add(ctx: Context, label: string, data: Uint8Array): undefined;
+export function stream_next(ctx: Context): Promise<{value: any} | {done: true}>;
+export function stream_write(ctx: Context, data: Uint8Array): undefined;
+export function stream_close(ctx: Context): undefined;