This is a breaking change to users who might be using Kopia as a library.
### Log Format
```json
{"t":"<timestamp-rfc-3389-microseconds>", "span:T1":"V1", "span:T2":"V2", "n":"<source>", "m":"<message>", /*parameters*/}
```
Where each record is associated with one or more spans that describe its scope:
* `"span:client": "<hash-of-username@hostname>"`
* `"span:repo": "<random>"` - random identifier of a repository connection (from `repo.Open`)
* `"span:maintenance": "<random>"` - random identifier of a maintenance session
* `"span:upload": "<hash-of-username@host:/path>"` - uniquely identifies upload session of a given directory
* `"span:checkpoint": "<random>"` - encapsulates each checkpoint operation during Upload
* `"span:server-session": "<random>"` -single client connection to the server
* `"span:flush": "<random>"` - encapsulates each Flush session
* `"span:maintenance": "<random>"` - encapsulates each maintenance operation
* `"span:loadIndex" : "<random>"` - encapsulates index loading operation
* `"span:emr" : "<random>"` - encapsulates epoch manager refresh
* `"span:writePack": "<pack-blob-ID>"` - encapsulates pack blob preparation and writing
(plus additional minor spans for various phases of the maintenance).
Notable points:
- Used internal zero allocation JSON writer for reduced memory usage.
- renamed `--disable-internal-log` to `--disable-repository-log` (controls saving blobs to repository)
- added `--disable-content-log` (controls writing of `content-log` files)
- all storage operations are also logged in a structural way and associated with the corresponding spans.
- all content IDs are logged in a truncated format (since first N bytes that are usually enough to be unique) to improve compressibility of logs (blob IDs are frequently repeated but content IDs usually appear just once).
This format should make it possible to recreate the journey of any single content throughout pack blobs, indexes and compaction events.
Use non-formatting logging functions for message without formatting.
For example, `log.Info("message")` instead of `log.Infof("message")`
Configure linter for printf-like functions
* logging: added logger wrappers for Broadcast and Prefix
* nit: moved max hash size to a named constant
* content: added internal logger
* content: replaced context-based logging with explicit Loggers
This will capture the logger.Logger associated with the context when
the repository is opened and will reuse it for all logs instead of
creating new logger for each log message.
The new logger will also write logs to the internal logger in addition
to writing to a log file/console.
* cli: allow decrypting all blobs whose names start with _
* maintenance: added logs cleanup
* cli: commands to view logs
* cli: log selected command on each write session
