Improve ``PresenterLifeCycleLinker`` public API.

[pedrovgs]

Fix #51. Now that we have accepted a pull request (#49) changing the visibility of the class PresenterLifeCycleLinker from default to public I have decided to improve this class usage. This is the list of improvements you will find in this pull request.

• Simplify the class usage reducing the number of methods needed to link the component lifecycle with the presenter lifecycle.
• Add javadoc.
• Add some guards related to the input params.
• Improve test coverage.
• Improve the project README to show how to use Rosie without extending from RosieActivity or RosieFragment.

[Serchinastico]

LGTM!

[pedrovgs]

I'll wait until travis pass the build and I'll merge this PR. Thanks!!