Add list-changed command (#98)

Allows to identify chart changes before actually running
lint or install commands. This can be useful in the following
cases:

* In a CI setup where kind clusters are spun up on the fly,
  this makes it possible to decide whether a cluster is necessary
  at all. A PR may only contain changes that are not relevant
  to any charts.
* By knowing upfront which charts have changed, it is
  possible to load a per-chart CI configuration which would
  allows us to determine the number of nodes needed in a kind
  cluster. For most charts, one node is enough, but in certain
  scenarios, especially for StatefulSets, we may want to test
  with pod anti-affinity where replicas have to be spread across
  multiple nodes.

Signed-off-by: Reinhard Nägele <unguiculus@gmail.com>

doc/ct.md

@@ -23,6 +23,7 @@ in given chart directories.
 * [ct install](ct_install.md)	 - Install and test a chart
 * [ct lint](ct_lint.md)	 - Lint and validate a chart
 * [ct lint-and-install](ct_lint-and-install.md)	 - Lint, install, and test a chart
+* [ct list-changed](ct_list-changed.md)	 - List changed charts
 * [ct version](ct_version.md)	 - Print version information
 
-###### Auto generated by spf13/cobra on 18-Jan-2019
+###### Auto generated by spf13/cobra on 31-Jan-2019

doc/ct_install.md

@@ -62,4 +62,4 @@ ct install [flags]
 
 * [ct](ct.md)	 - The Helm chart testing tool
 
-###### Auto generated by spf13/cobra on 18-Jan-2019
+###### Auto generated by spf13/cobra on 31-Jan-2019

doc/ct_lint-and-install.md

@@ -61,4 +61,4 @@ ct lint-and-install [flags]
 
 * [ct](ct.md)	 - The Helm chart testing tool
 
-###### Auto generated by spf13/cobra on 18-Jan-2019
+###### Auto generated by spf13/cobra on 31-Jan-2019

doc/ct_lint.md

@@ -65,4 +65,4 @@ ct lint [flags]
 
 * [ct](ct.md)	 - The Helm chart testing tool
 
-###### Auto generated by spf13/cobra on 18-Jan-2019
+###### Auto generated by spf13/cobra on 31-Jan-2019

doc/ct_list-changed.md

@@ -0,0 +1,31 @@
+## ct list-changed
+
+List changed charts
+
+### Synopsis
+
+"List changed charts based on configured charts directories,
+"remote, and target branch
+
+```
+ct list-changed [flags]
+```
+
+### Options
+
+```
+      --chart-dirs strings        Directories containing Helm charts. May be specified multiple times
+                                  or separate values with commas (default [charts])
+      --config string             Config file
+      --excluded-charts strings   Charts that should be skipped. May be specified multiple times
+                                  or separate values with commas
+  -h, --help                      help for list-changed
+      --remote string             The name of the Git remote used to identify changed charts (default "origin")
+      --target-branch string      The name of the target branch used to identify changed charts (default "master")
+```
+
+### SEE ALSO
+
+* [ct](ct.md)	 - The Helm chart testing tool
+
+###### Auto generated by spf13/cobra on 31-Jan-2019

doc/ct_version.md

@@ -20,4 +20,4 @@ ct version [flags]
 
 * [ct](ct.md)	 - The Helm chart testing tool
 
-###### Auto generated by spf13/cobra on 18-Jan-2019
+###### Auto generated by spf13/cobra on 31-Jan-2019