tracing-journald 0.3.0

This is a breaking release which changes the format in which span fields
are output to journald. Previously, span field names were prefixed with the
depth of the span in the current trace tree. However, these prefixes are
unnecessary, as journald has built in support for duplicated field names.

See PR #1986 for details on this change.

Changed

• Removed span field prefixes (#1986)
• Renamed S{num}_NAME fields to SPAN_NAME (#1986)

Fixed

• Fixed broken links in documentation (#2077)

Thanks to @wiktorsikora and @ben0x539 for contributing to this release!