Renamed Stream.value to 'contents' to avoid name clashes

[jlstevens]

A parameter called value would be very natural to use in a stream making it likely to clash with the value property. Renaming this property to contents should help avoid potential name clashes and confusion.

Ready to merge.

[philippjfr]

Looks good, contents is much less likely to clash than value. I'll merge when tests pass.

[jlstevens]

Push build has passed. I had to restart one of the pr builds due to a transient error - you can wait for that to pass but I don't think you need to!