Add tags.Extract() func

tags/tags.go

@@ -0,0 +1,22 @@
+package tags
+
+import (
+	"github.com/kylemcc/twitter-text-go/extract"
+)
+
+func Extract(body string) []string {
+	matches := extract.ExtractHashtags(body)
+	tags := map[string]bool{}
+	for i := range matches {
+		// Second value (whether or not there's a hashtag) ignored here, since
+		// we're only extracting hashtags.
+		ht, _ := matches[i].Hashtag()
+		tags[ht] = true
+	}
+
+	resTags := make([]string, 0)
+	for k := range tags {
+		resTags = append(resTags, k)
+	}
+	return resTags
+}