remove node-fetch as runtime dependency

src/fetchers/fetch.ts

@@ -0,0 +1,22 @@
+/**
+ * This file is a very relaxed definition of the fetch api
+ * Only containing what we need for it to function.
+ */
+
+export type FetchOps = {
+  headers: Record<string, string>;
+  method: string;
+  body: any;
+};
+
+export type FetchHeaders = {
+  get(key: string): string | undefined;
+};
+
+export type FetchReply = {
+  text(): Promise<string>;
+  json(): Promise<any>;
+  headers: FetchHeaders;
+};
+
+export type FetchType = (url: string, ops?: FetchOps) => Promise<FetchReply>;