feat: support HTTP/SaaS function trigger

.gitignore

@@ -4,4 +4,5 @@ dist
 coverage
 .vscode
 .glee
-.next
+.next
+glee-test

.prettierignore

@@ -0,0 +1 @@
+*.md

.prettierrc

@@ -0,0 +1,6 @@
+{
+  "semi": false,
+  "singleQuote": true,
+  "trailingComma": "es5",
+  "printWidth": 100
+}

docs/functions.md

@@ -37,6 +37,7 @@ export default async function (event) {
 |---|---|---|
 |send|array<[OutboundMessage](#anatomy-of-an-outbound-message)>|A list of outbound messages to send when the processing of the inbound event has finished. All clients subscribed to the given channel/topic will receive the message.
 |reply|array<[OutboundMessage](#anatomy-of-an-outbound-message)>|A list of outbound messages to send as a reply when the processing of the inbound event has finished. This is useful when the target of your message is the sender of the inbound event. Note, however, that this only works when you're running Glee as a server. For example, using `reply` when receiving a WebSocket message is fine and the reply will exclusively go to the client that sent the message. However, if you're receiving a message from an MQTT broker, `reply` will work exactly the same way as `send` above, and will send the message to all the clients subscribed to the given channel/topic.
+|invoke|array<[InvokeRequest](#anatomy-of-an-invoke-message)>|A list of requests for reaching an HTTP/HTTPS endpoint. This is useful when you have a software as a service (SaaS) function and want it to be treated as one of Glee's functions.
 
 
 ##### Anatomy of an outbound message
@@ -48,6 +49,17 @@ export default async function (event) {
 |channel|string|The channel/topic you want to send the message to. Defaults to `event.channel`, i.e., the same channel as the received event.
 |server|string|The server/broker you want to send the message to. Defaults to `event.serverName`, i.e., the same server as the received event.
 
+##### Anatomy of an invoke message
+
+|Attribute|Type|Description|
+|---|---|---|
+|url|string|The URL of your HTTP/SaaS end-point.
+|headers|object<string,string>|The headers/metadata of the message you want to send.
+|method|string|The HTTP method that you want your endpoint to be called with.
+|ignoreResponse|boolean|By default, Glee assumes that the response is in JSON format and adheres to the [Functions](#functions) return type structure. If you do not wish for Glee to process the response, you can set the this option to `false`.
+
+> NOTE: Glee uses [got](https://github.com/sindresorhus/got) under the hood. Therefore, you have the ability to personalize your request with any options that [got](https://github.com/sindresorhus/got#documentation) supports.
+
 ## How does Glee know which function it should execute?
 
 Glee reads your `asyncapi.yaml` file and searches for all the `publish` operations containing an `operationId` attribute. The `operationId` serves as a mechanism to bind a given operation to a specific function file. For instance, given the folowing AsyncAPI definition:
@@ -61,4 +73,23 @@ channels:
       ...
 ```
 
-Glee maps the `onHello` operation to the `functions/onHello.js` file.
+Glee maps the `onHello` operation to the `functions/onHello.js` file.
+
+## Using FaaS functions as glee functions
+
+Glee can treat your FaaS function as its own by setting `operationId` to your function URL and customizing it with the `x-glee-invoke` extension:
+
+```yaml
+channels:
+  hello:
+    publish:
+      operationId: https://domain.come/path/to/your/function
+      x-glee-invoke:
+        method: get
+        headers:
+          Content-Type: application/json
+        ignoreResponse: true # By default, Glee processes the response and raises an error if it does not conform to the format specified by [functions](#functions) return type.
+      ...
+
+```
+> NOTE: Avoid including authentication details in the asyncapi file. Instead, use the invoke option in [functions](#functions) return to authenticate your call.