Added system hooks link to doc index

Fix API return codes

Conflicts:
	doc/api/projects.md
	spec/requests/api/projects_spec.rb

Capistrano deploy example

Autofocus to username input (LDAP login).

Additional Admin APIs

Allow connection to Redis via unix socket

Refactor README to split production/development environments

All the info to return codes from the API functions are available in the `README.md` file as suggested.

Allow connection to Redis via unix socket, using
unix:/var/run/redis/redis.sock for example.

Default behaviour does not change, except that the full Redis URL must
be configured, with redis:// for tcp or unix: for unix socket.

Use secure protocol

Added methods to manage project deploy keys via API

Added methods to manage system hooks from API

Update README with references to versions.

Fix routing error

It should fix #2598.

It is linked to #2598.