Initial bootrap of application

- Creates scaffold for router and server
- Main program set up for environment, OS signal listener
- Makefile generic commands

internal/http/middleware.go

@@ -0,0 +1,16 @@
+package http
+
+import "net/http"
+
+// setResponseHeaders is a middleware that accepts a map[string]string of headers:values and sets them for all responses.
+func setResponseHeaders(headers map[string]string) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			for header, value := range headers {
+				w.Header().Set(header, value)
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}