Remove the legacy multirepositories system

Signed-off-by: Aymeric Brisse <aymeric.brisse@perfect-memory.com>
Use YARD::Rake::YardocTask in Rakefile

Signed-off-by: Aymeric Brisse <aymeric.brisse@perfect-memory.com>
Update Spira.using_repository to ensure the repository restore

Signed-off-by: Aymeric Brisse <aymeric.brisse@perfect-memory.com>
Merge commit '336ff9dd064b85a133401c8952a955605e1cf0ec' into develop
Enhance README.md 

* Add ``` for ruby syntax
* Add Spira.repository= in the examples

Signed-off-by: Aymeric Brisse <aymeric.brisse@perfect-memory.com>