Add documentation and documentation testing

docs/src/isConnected.md.ejs

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+## isConnected
+
+`isConnected(): boolean`
+
+Checks if the RippleAPI instance is connected to its server(s).
+
+### Parameters
+
+This method has no parameters.
+
+### Return Value
+
+This method returns `true` if connected and `false` if not connected.
+
+### Example
+
+```javascript
+return api.isConnected();
+```
+
+```json
+true
+```