Add kpod diff command

kpod diff reports on differences between two layers, specified as
layer IDs, containers, or images.  In the case of containers or
images, kpod diff produces a diff for the top layer

Signed-off-by: Ryan Cole <rcyoalne@gmail.com>

docs/kpod-diff.1.md

@@ -0,0 +1,45 @@
+% kpod(1) kpod-diff - Inspect changes on a container or image's filesystem
+% Dan Walsh
+# kpod-diff "1" "August 2017" "kpod"
+
+## NAME
+kpod diff - Inspect changes on a container or image's filesystem
+
+## SYNOPSIS
+**kpod** **diff** [*options* [...]] NAME
+
+## DESCRIPTION
+Displays changes on a container or image's filesystem.  The container or image will be compared to its parent layer
+
+## OPTIONS
+
+**--json**
+
+Format output as json
+
+
+## EXAMPLE
+
+kpod diff redis:alpine
+C /usr
+C /usr/local
+C /usr/local/bin
+A /usr/local/bin/docker-entrypoint.sh
+
+kpod diff --json redis:alpine
+{
+  "changed": [
+    "/usr",
+    "/usr/local",
+    "/usr/local/bin"
+  ],
+  "added": [
+    "/usr/local/bin/docker-entrypoint.sh"
+  ]
+}
+
+## SEE ALSO
+kpod(1)
+
+## HISTORY
+August 2017, Originally compiled by Ryan Cole <rycole@redhat.com>