- Introduce RocException. Use it for system errors instead
  of Exception or IOException.

- Update "throws" clauses. Explicitly list only checked exceptions.
  Don't list unchecked. But document all exceptions.

- Rework C assertions. Remove assertions for failures caused by
  incorrect calls of C code from Java code. Instead, throw Java
  exceptions. Keep assertions only for internal violations on the
  C side.

- Rework C helpers. All helpers return bool. If they return false,
  they also throw a java exception with failure details. Also make
  helpers more high level to simplify code that use them.

- Remove boilerplate C helpers for enums, instead add a single
  function read_enum_field() an use it for all enums.

- Improvements in logger on C side: cache java log levels, properly
  use global references.

- Enable assertions in release builds too.

- Additional validation in MediaEncoding builder to catch more
  user errors earlier.