[core] Edit documentation on TransactionManager.begin(boolean)
Introduce new Atomic attributes
Simplify logic based on possible atomic values
[test-backend-jvstm-common] Add tests for flattenNested
[backend-jvstm-common] Implement support for flattenNested.

  * Also, fix creation of nested read-only in write tx: Actually create a
    nested write (because we need the write-set), but use setReadOnly() to
    enforce the expected behavior.
Merge pull request #104 from smmf/feature/issue-99-review-atomic-annotation-properties

Feature/review atomic annotation properties

  * Fixes #99