refactor(helpers): separate functions into files (#667)

* refactor(helpers): separate functions into files

* idk

* idk

src/helpers/guilds/guild_banner_url.ts

@@ -0,0 +1,19 @@
+import { Guild } from "../../structures/mod.ts";
+import { ImageFormats, ImageSize } from "../../types/mod.ts";
+import { endpoints } from "../../util/constants.ts";
+import { formatImageURL } from "../../util/utils.ts";
+
+/** The full URL of the banner from Discords CDN. Undefined if no banner is set. */
+export function guildBannerURL(
+  guild: Guild,
+  size: ImageSize = 128,
+  format?: ImageFormats,
+) {
+  return guild.banner
+    ? formatImageURL(
+      endpoints.GUILD_BANNER(guild.id, guild.banner),
+      size,
+      format,
+    )
+    : undefined;
+}