Add spec.homepage field to the plugin manifest (#158)

* Add `spec.homepage` field to the plugin manifest

The `spec.homepage` field of the plugin manifest defines the url of the
plugin project homepage. The field value should be a valid url.

In addition, if the `spec.homepage` field is defined in plugin manifest,
`kubectl krew info` command displays that field value as HOMEPAGE as follows:

    $ kubectl krew info krew
    NAME: krew
    URI: https://storage.googleapis.com/krew/v0.2.1/krew.tar.gz
    SHA256: dc2f2e1ec8a0acb6f3e23580d4a8b38c44823e948c40342e13ff6e8e12edb15a
    VERSION: v0.2.1
    HOMEPAGE: https://github.com/GoogleContainerTools/krew
    ...

* Reorder the output fields of `krew info` command

By this change, the output fields of `krew info` command are reordered as follows:
```
$ out/bin/krew-darwin_amd64 info krew
NAME: krew
URI: https://storage.googleapis.com/krew/v0.2.1/krew.tar.gz
SHA256: dc2f2e1ec8a0acb6f3e23580d4a8b38c44823e948c40342e13ff6e8e12edb15a
VERSION: v0.2.1
HOMEPAGE: https://github.com/GoogleContainerTools/krew
CAVEATS:
\
...
```

* Edit testdata to add homepage field

* Remove validating code for homepage field

cmd/krew/cmd/info.go

@@ -68,12 +68,15 @@ func printPluginInfo(out io.Writer, plugin index.Plugin) {
 			fmt.Fprintf(out, "SHA256: %s\n", platform.Sha256)
 		}
 	}
-	if plugin.Spec.Description != "" {
-		fmt.Fprintf(out, "DESCRIPTION: \n%s\n", plugin.Spec.Description)
-	}
 	if plugin.Spec.Version != "" {
 		fmt.Fprintf(out, "VERSION: %s\n", plugin.Spec.Version)
 	}
+	if plugin.Spec.Homepage != "" {
+		fmt.Fprintf(out, "HOMEPAGE: %s\n", plugin.Spec.Homepage)
+	}
+	if plugin.Spec.Description != "" {
+		fmt.Fprintf(out, "DESCRIPTION: \n%s\n", plugin.Spec.Description)
+	}
 	if plugin.Spec.Caveats != "" {
 		fmt.Fprintln(out, prepCaveats(plugin.Spec.Caveats))
 	}

docs/DEVELOPER_GUIDE.md

@@ -109,6 +109,7 @@ spec:
       to: "."               # '.' refers to the root of plugin install directory
     bin: "./kubectl-foo"  # path to the plugin executable after copying files above
   shortDescription: Prints the environment variables.
+  homepage: https://github.com/GoogleContainerTools/krew # optional, url for the project homepage
   # (optional) use caveats field to show post-installation recommendations
   caveats: |
     This plugin needs the following programs:

pkg/index/indexscanner/testdata/testindex/plugins/foo.yaml

@@ -33,4 +33,4 @@ spec:
       matchLabels:
         os: "windows"
   shortDescription: "exists"
-
+  homepage: "https://example.com/foo"

pkg/index/types.go

@@ -33,6 +33,7 @@ type PluginSpec struct {
 	ShortDescription string `json:"shortDescription,omitempty"`
 	Description      string `json:"description,omitempty"`
 	Caveats          string `json:"caveats,omitempty"`
+	Homepage         string `json:"homepage,omitempty"`
 
 	Platforms []Platform `json:"platforms,omitempty"`
 }

pkg/index/validate_test.go

@@ -112,6 +112,7 @@ func TestPlugin_Validate(t *testing.T) {
 					ShortDescription: "short",
 					Description:      "",
 					Caveats:          "",
+					Homepage:         "",
 					Platforms: []Platform{{
 						Head:     "http://example.com",
 						URI:      "",