Addressed regression of private repository documentation.

This adds back in the references to private repositories and
provides some refactoring to the Working with repositories
documentation including updating references to the "Central"
registry to Docker.io.

It also:

* Fixes some links and references to Central Index
* Fixes anchors in other files to updated titles in Working with Repositories.
* Renamed Central Index in the remaining places.
* Updated terms documentation to reflect Docker.io
* Updated some Docker Index naming to be consistent.
* Updates menu labels and hyperlinks.

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)

docs/sources/reference/api/archive/docker_remote_api_v1.0.md

@@ -734,7 +734,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index
+Search for an image on [Docker.io](https://index.docker.io)
 
     **Example request**:
 

docs/sources/reference/api/archive/docker_remote_api_v1.1.md

@@ -745,7 +745,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index
+Search for an image on [Docker.io](https://index.docker.io)
 
     **Example request**:
 

docs/sources/reference/api/archive/docker_remote_api_v1.2.md

@@ -772,7 +772,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index
+Search for an image on [Docker.io](https://index.docker.io)
 
     **Example request**:
 

docs/sources/reference/api/archive/docker_remote_api_v1.3.md

@@ -821,7 +821,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index
+Search for an image on [Docker.io](https://index.docker.io)
 
     **Example request**:
 

docs/sources/reference/api/archive/docker_remote_api_v1.4.md

@@ -866,7 +866,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index
+Search for an image on [Docker.io](https://index.docker.io)
 
     **Example request**:
 

docs/sources/reference/api/archive/docker_remote_api_v1.5.md

@@ -871,7 +871,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index
+Search for an image on [Docker.io](https://index.docker.io)
 
     **Example request**:
 

docs/sources/reference/api/archive/docker_remote_api_v1.6.md

@@ -976,7 +976,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index
+Search for an image on [Docker.io](https://index.docker.io)
 
     **Example request**:
 

docs/sources/reference/api/archive/docker_remote_api_v1.7.md

@@ -902,7 +902,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index.
+Search for an image on [Docker.io](https://index.docker.io).
 
 > **Note**:
 > The response keys have changed from API v1.6 to reflect the JSON

docs/sources/reference/api/archive/docker_remote_api_v1.8.md

@@ -944,7 +944,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index.
+Search for an image on [Docker.io](https://index.docker.io).
 
 > **Note**:
 > The response keys have changed from API v1.6 to reflect the JSON

docs/sources/reference/api/docker-io_api.md

@@ -1,12 +1,12 @@
-page_title: Index API
-page_description: API Documentation for Docker Index
-page_keywords: API, Docker, index, REST, documentation
+page_title: Docker.io API
+page_description: API Documentation for the Docker.io API
+page_keywords: API, Docker, index, REST, documentation, Docker.io, registry
 
-# Docker Index API
+# Docker.io API
 
 ## Introduction
 
-- This is the REST API for the Docker index
+- This is the REST API for [Docker.io](http://index.docker.io).
 - Authorization is done with basic auth over SSL
 - Not all commands require authentication, only those noted as such.
 

docs/sources/reference/api/docker_remote_api_v1.10.md

@@ -934,7 +934,7 @@ Tag the image `name` into a repository
 
 `GET /images/search`
 
-Search for an image in the docker index.
+Search for an image on [Docker.io](https://index.docker.io).
 
 > **Note**:
 > The response keys have changed from API v1.6 to reflect the JSON

docs/sources/reference/api/docker_remote_api_v1.11.md

@@ -937,7 +937,7 @@ Remove the image `name` from the filesystem
 
 `GET /images/search`
 
-Search for an image in the docker index.
+Search for an image on [Docker.io](https://index.docker.io).
 
 > **Note**:
 > The response keys have changed from API v1.6 to reflect the JSON

docs/sources/reference/api/docker_remote_api_v1.9.md

@@ -947,7 +947,7 @@ Tag the image `name` into a repository
 
 `GET /images/search`
 
-Search for an image in the docker index.
+Search for an image on [Docker.io](https://index.docker.io).
 
 > **Note**:
 > The response keys have changed from API v1.6 to reflect the JSON