Choose a strategy for semantic versioning of the java artifacts

We need to decide which java packages are "internal" and we are free to refactor without going up a major revision, and which are part of our public API and require strict semantic versioning. We need to then reflect this in the maven enforcer that detects these changes.

**Reporter**: [Alex Levenson](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=alexlevenson) / @isnotinvain

_{**Note**: *This issue was originally created as [PARQUET-31](https://issues.apache.org/jira/browse/PARQUET-31). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Start by reviewing the Java package structure, the Maven enforcer configuration, and the migration documentation linked from the issue for PARQUET-31 context. Done means the public and internal package boundaries are agreed and the enforcer reflects the chosen semantic-versioning rules.

Written by the indexing model from the issue text.