Convert CLI to urfave v2

Followed the Migration Guide at https://cli.urfave.org/migrate-v1-to-v2/
The major changes not pointed out in the migration guide are:
- context.Args() no longer produces a []slice, so context.Args().Slice()
  in substitued
- All cli.Global***** are deprecated (the migration guide is somewhat
  unclear on this)

Signed-off-by: Derek Nola <derek.nola@suse.com>

Vendor in urfave cli/v2

Signed-off-by: Derek Nola <derek.nola@suse.com>

Fix NewStringSlice calls

Signed-off-by: Derek Nola <derek.nola@suse.com>

vendor/github.com/xrash/smetrics/hamming.go

@@ -0,0 +1,25 @@
+package smetrics
+
+import (
+	"fmt"
+)
+
+// The Hamming distance is the minimum number of substitutions required to change string A into string B. Both strings must have the same size. If the strings have different sizes, the function returns an error.
+func Hamming(a, b string) (int, error) {
+	al := len(a)
+	bl := len(b)
+
+	if al != bl {
+		return -1, fmt.Errorf("strings are not equal (len(a)=%d, len(b)=%d)", al, bl)
+	}
+
+	var difference = 0
+
+	for i := range a {
+		if a[i] != b[i] {
+			difference = difference + 1
+		}
+	}
+
+	return difference, nil
+}