[Short-circuit API] Add some javadoc.

[colinepiloquet]

Please check if the PR fulfills these requirements

• [X] The commit message follows our guidelines
• [X] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem?

No

What kind of change does this PR introduce?

Docs update

What is the current behavior?

A lot of javadoc is missing.

What is the new behavior (if this is a feature change)? I've tried to add a short description for every public class or method.

Does this PR introduce a breaking change or deprecate an API?

• [ ] Yes
• [X] No