Add support for stopwords, metrics & stats (#179)

* feat: retrieve & upsert stopwords

* feat: retrieve & delete a stopword set

* test-integration: retrieve & upsert stopwords sets

* test-integration: retrieve & delete a stopword set

* test-integration: single collection & multi search with stopwords

* fix: multi-search integration test

* feat: retrieve API stats

* fix: lint

* feat: retrieve cluster metrics

* fix: bump to v2 after git rebase

* update README: stopwords, metrics & stats

README.md

@@ -399,6 +399,34 @@ client.Collection("products").Synonyms().Retrieve(context.Background())
 client.Collection("products").Synonym("coat-synonyms").Delete(context.Background())
 ```
 
+### Create or update a stopwords set
+
+```go
+	stopwords := &api.StopwordsSetUpsertSchema{
+		Locale:    pointer.String("en"),
+		Stopwords: []string{"Germany", "France", "Italy", "United States"},
+	}
+	client.Stopwords().Upsert(context.Background(), "stopword_set1", stopwords)
+```
+
+### Retrieve a stopwords set
+
+```go
+client.Stopword("stopword_set1").Retrieve(context.Background())
+```
+
+### List all stopwords sets
+
+```go
+client.Stopwords().Retrieve(context.Background())
+```
+
+### Delete a stopwords set
+
+```go
+client.Stopword("stopword_set1").Delete(context.Background())
+```
+
 ### Create or update a preset
 
 ```go
@@ -445,6 +473,18 @@ client.Operations().Snapshot(context.Background(), "/tmp/typesense-data-snapshot
 client.Operations().Vote(context.Background())
 ```
 
+### Cluster Metrics
+
+```go
+client.Metrics().Retrieve(context.Background())
+```
+
+### API Stats
+
+```go
+client.Stats().Retrieve(context.Background())
+```
+
 ## Contributing
 
 Bug reports and pull requests are welcome on GitHub at https://github.com/typesense/typesense-go.