Move to yaml-based configuration

This commit updates the configuration to be yaml-based and updates the
configuration to read in a yaml file.

internal/config/validators/int.go

@@ -0,0 +1,32 @@
+package validators
+
+import (
+	"strconv"
+
+	"github.com/pkg/errors"
+)
+
+func ValidatePositive(value *int, dflt string) (err error) {
+	if *value == 0 && dflt != "" {
+		v, err := strconv.ParseInt(dflt, 10, 64)
+		if err != nil {
+			return err
+		}
+		*value = int(v)
+	}
+	if *value <= 0 {
+		return errors.Errorf("%d is not a positive value", *value)
+	}
+	return nil
+}
+
+func ValidatePort(value *uint16, dflt string) (err error) {
+	if *value == 0 && dflt != "" {
+		v, err := strconv.ParseUint(dflt, 10, 16)
+		if err != nil {
+			return err
+		}
+		*value = uint16(v)
+	}
+	return nil
+}