Massive restructure of plugin API

plug-api/silverbullet-syscall/syscall.ts

@@ -0,0 +1,16 @@
+declare global {
+  function syscall(name: string, ...args: any[]): Promise<any>;
+}
+
+// This is the case when running tests only, so giving it a dummy syscall function
+if (typeof self === "undefined") {
+  // @ts-ignore: test
+  // deno-lint-ignore no-global-assign
+  self = {
+    syscall: () => {
+      throw new Error("Not implemented here");
+    },
+  };
+}
+
+export const syscall = self.syscall;