Fixed javadoc warnings for model project.
Fixed javadoc warnings in rio-api project.
Fixed javadoc warnings in query package.
Merged in javadoc-fixes (pull request #99)

Fixes for Javadoc warnings in the console output for CI 103
Fixed javadoc warnings in queryalgebra-model, includes a minor code change.
Fixed javadoc warnings in sail-api project.
Fixed javadoc warning in TurtleUtil.
Fixed javadoc warning in NQuadsWriter.
Merged in javadoc-fix (pull request #100)

Fixes for more javadoc warnings spotted in CI Build #104 console output.