Tweak logging output.
Only monitor clients with successful queries.
Allow for arbitrary characters in values.
Make file::open return its error string.
Support reading from stdin via '-' as filename.
Add missing error case.
Make mkdir more permissive in its return code.

In addition to enriching the return value of vast::mkdir, we also made it more
permissive: we no longer return a failure if the directory already exists, only
if we actually failed to create it. This is important because of TOCTTOU
problems with the file systems: if multiple actors attempt to construct the
same directory, it will no longer fail.
Make serialization/compression wrappers more monadic.
A few more logging and error propagation tweaks.
Support reading multiple concatenated Bro logs.

This comes in especially handy when reading goop from STDIN.

We also added an auto-detection mechanism that looks at the first value type of
a Bro log. If it is a timestamp, we use it automatically for the timestamp of
the event. It's still possible to manually select a timestamp field with the
option --ingest.time-field.