[crac] RFR: Refactored javadocs with additional details

[Radim Vansa]

Improve API documentation.

-------------

Commit messages:
 - Refactored javadocs with additional details

Changes: https://git.openjdk.org/crac/pull/65/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=65&range=00
  Stats: 160 lines in 6 files changed: 105 ins; 46 del; 9 mod
  Patch: https://git.openjdk.org/crac/pull/65.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/65/head:pull/65

PR: https://git.openjdk.org/crac/pull/65