chore: move all source files to new folder

Update the project structure to move all golang files to a new `src/`
folder. This keeps all the code located in the same place and easier to
work with.
Update the Makefile and goreleaser config to continue to work with the new
folder structure.

src/cfg/cfg.go

@@ -0,0 +1,48 @@
+package cfg
+
+import (
+	"flag"
+	"fmt"
+	"os"
+)
+
+const (
+	minServerPort = 1000
+	maxServerPort = 65535
+)
+
+type AppSettings struct {
+	VersionMode    bool
+	MetricsPort    int
+	Fail2BanDbPath string
+}
+
+func Parse() *AppSettings {
+	appSettings := &AppSettings{}
+	flag.BoolVar(&appSettings.VersionMode, "version", false, "show version info and exit")
+	flag.IntVar(&appSettings.MetricsPort, "port", 9191, "port to use for the metrics server")
+	flag.StringVar(&appSettings.Fail2BanDbPath, "db", "", "path to the fail2ban sqlite database")
+
+	flag.Parse()
+	appSettings.validateFlags()
+	return appSettings
+}
+
+func (settings *AppSettings) validateFlags() {
+	var flagsValid = true
+	if !settings.VersionMode {
+		if settings.Fail2BanDbPath == "" {
+			fmt.Println("missing flag 'db'")
+			flagsValid = false
+		}
+		if settings.MetricsPort < minServerPort || settings.MetricsPort > maxServerPort {
+			fmt.Printf("invalid server port, must be within %d and %d (found %d)\n",
+				minServerPort, maxServerPort, settings.MetricsPort)
+			flagsValid = false
+		}
+	}
+	if !flagsValid {
+		flag.Usage()
+		os.Exit(1)
+	}
+}