Break the fs package up into smaller parts.

The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.

The new code layout is documented in CONTRIBUTING.

fs/parseduration.go

@@ -0,0 +1,68 @@
+package fs
+
+import (
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Duration is a time.Duration with some more parsing options
+type Duration time.Duration
+
+// Turn Duration into a string
+func (d Duration) String() string {
+	return time.Duration(d).String()
+}
+
+// We use time conventions
+var ageSuffixes = []struct {
+	Suffix     string
+	Multiplier time.Duration
+}{
+	{Suffix: "ms", Multiplier: time.Millisecond},
+	{Suffix: "s", Multiplier: time.Second},
+	{Suffix: "m", Multiplier: time.Minute},
+	{Suffix: "h", Multiplier: time.Hour},
+	{Suffix: "d", Multiplier: time.Hour * 24},
+	{Suffix: "w", Multiplier: time.Hour * 24 * 7},
+	{Suffix: "M", Multiplier: time.Hour * 24 * 30},
+	{Suffix: "y", Multiplier: time.Hour * 24 * 365},
+
+	// Default to second
+	{Suffix: "", Multiplier: time.Second},
+}
+
+// ParseDuration parses a duration string. Accept ms|s|m|h|d|w|M|y suffixes. Defaults to second if not provided
+func ParseDuration(age string) (time.Duration, error) {
+	var period float64
+
+	for _, ageSuffix := range ageSuffixes {
+		if strings.HasSuffix(age, ageSuffix.Suffix) {
+			numberString := age[:len(age)-len(ageSuffix.Suffix)]
+			var err error
+			period, err = strconv.ParseFloat(numberString, 64)
+			if err != nil {
+				return time.Duration(0), err
+			}
+			period *= float64(ageSuffix.Multiplier)
+			break
+		}
+	}
+
+	return time.Duration(period), nil
+}
+
+// Set a Duration
+func (d *Duration) Set(s string) error {
+	duration, err := ParseDuration(s)
+	if err != nil {
+		return err
+	}
+	*d = Duration(duration)
+	return nil
+}
+
+// Type of the value
+func (d Duration) Type() string {
+	return "time.Duration"
+}