frontend: Guarantee that no async messages are sent before startup finished.
ReleaseNotes: Added some notes about compatibility.

That is, mention that there are no compatibility guarantees at the moment (pre
1.0 versions).
proto: Fixed/clarified authentication handshake options during startup.

The server may request further authentication information from the client
before sending an OK status.
strbuf utils: Clarified handling of binary data.
frontend, proto: Include the response data type in query replies.

For that purpose, use the newly added CONNECTION_DATA status instead of
CONNECTION_OK for query replies and include the data type as the first field
in the message body. The type is the same as the respective command type.
frontend/proto: Let CONNECTION_DATA not replace CONNECTION_ERROR.

Instead, reserve some space for groups of status/state codes and then use a
new number / block for CONNECTION_DATA.
frontend/proto: Include the log priority in LOG messages.

The priority is encoded as 32 bit integer in network byte order and added as a
separate field before the actual log message.

The 'sysdb' client now handles LOG messages accordingly and prefixes the
message with a string describing the priority.
frontend, sysdb: Correctly handle empty queries.

Let the frontend send back a DATA message even on empty queries to make sure
the client sees the expected reply.

Let sysdb handle empty replies correctly and also not print any errors on
empty replies (successful command not returning any data).
utils strbuf: Renamed buffer variables from 'strbuf' to 'buf'.
utils strbuf: Added 'min_size' to be considered when shrinking the buffer.

It's set to the initial size of the buffer (or 64). The idea is that the
initial size should provide an estimate of a reasonable size and shrinking the
buffer below that size causes unecessary churn.

For example, this is important for the frontend's command handlers which
usually need a large buffer size but initial writes to the buffer may be
small.
utils strbuf: Exponentially increase the buffer size.

That'll make sure that lots of small writes don't result in lots of memory
reallocations.
store: Don't wrap JSON serialized LIST replies in a separate object.

Previously, the reply was {"hosts": [<list>]} while now it's just the list.
This way, the response format matches that of other commands which return host
lists.
store: Fixed JSON for serialized time-series.

Each field needs a name, add the name to the "data" field.