refactor(api): create a new structure for the Go api (#94)

* refactor(api): create a new structure for the Go api

* refactor(api): update the way keyFile parameter is managed

api/config.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+// Config defines the configuration available under the /config endpoint
+type Config struct {
+	Swarm        bool     `json:"swarm"`
+	HiddenLabels pairList `json:"hiddenLabels"`
+}
+
+// newConfig creates a new Config from command flags
+func newConfig(swarm bool, labels pairList) Config {
+	return Config{
+		Swarm:        swarm,
+		HiddenLabels: labels,
+	}
+}
+
+// configurationHandler defines a handler function used to encode the configuration in JSON
+func configurationHandler(w http.ResponseWriter, r *http.Request, c Config) {
+	json.NewEncoder(w).Encode(c)
+}