feat: add headers to REST options (#79)

* headers option is added to REST options

* fixed linting

* fixed typing

* changed the order of header assignment

index.d.ts

@@ -519,6 +519,7 @@ declare namespace Dysnomia {
     disableLatencyCompensation?: boolean;
     domain?: string;
     port?: string;
+    headers?: Record<string, number | string | string[]>;
     https?: boolean;
     latencyThreshold?: number;
     ratelimiterOffset?: number;

lib/Client.js

@@ -105,6 +105,7 @@ class Client extends EventEmitter {
     * @arg {Boolean} [options.rest.https=true] Whether to make requests to the Discord API over HTTPS (true) or HTTP (false)
     * @arg {Number} [options.rest.latencyThreshold=30000] The average request latency at which Dysnomia will start emitting latency errors
     * @arg {Number} [options.rest.port] The port to use for API requests. Defaults to 443 (HTTPS) or 80 (HTTP)
+    * @arg {Object} [options.rest.headers] Headers to be appended in REST requests
     * @arg {Number} [options.rest.ratelimiterOffset=0] A number of milliseconds to offset the ratelimit timing calculations by
     * @arg {Number} [options.rest.requestTimeout=15000] A number of milliseconds before REST requests are considered timed out
     * @arg {Boolean} [options.restMode=false] Whether to enable getting objects over REST. Even with this option enabled, it is recommended that you check the cache first before using REST

lib/rest/RequestHandler.js

@@ -82,6 +82,9 @@ class RequestHandler {
                 let finalURL = url;
 
                 try {
+                    if(this.options.headers) {
+                        Object.assign(headers, this.options.headers);
+                    }
                     if(auth) {
                         headers.Authorization = this._client._token;
                     }