Add GuildMember.permissionsIn and make ChannelResolvables more lenient

src/structures/GuildMember.js

@@ -167,6 +167,19 @@ class GuildMember {
     return new EvaluatedPermissions(this, permissions);
   }
 
+  /**
+   * Returns `guildChannel.permissionsFor(guildMember)`. Returns evaluated permissions for a member in a guild channel.
+   * @param {ChannelResolvable} guildChannel the guild channel to use as context
+   * @returns {?EvaluatedPermissions}
+   */
+  permissionsIn(guildChannel) {
+    guildChannel = this.client.resolver.resolveChannel(guildChannel);
+    if (!guildChannel) {
+      throw new Error('supply a channel resolvable that resolves to a GuildChannel!');
+    }
+    return guildChannel.permissionsFor(this);
+  }
+
   /**
    * Checks if any of the member's roles have a permission
    * @param {PermissionResolvable} permission The permission to check for