Improve byChunk, lockingTextWriter doc

Make byChunk, lockingTextWriter return opaque types (but keep those
types public for backward compatibility).
Add byChunk range example.
Also document that ByLine's primitives can throw StdioException.
Add comments for ranges that are no longer documented
lockingTextWriter should not be a @property
Merge pull request #1448 from ntrel/stdio-range-doc

Improve byChunk, lockingTextWriter doc