chg: [unifiedlog_iterator] support jsonl output and more params

[cvandeplas]

This change brings support for jsonl output.
The output can be saved to a file, or to the standard output.
If the user does not specify the output format as -f parameter, it defaults to autodetect it based on the filename.
The user can also specify to --append append or not (default). I found the previous default of appending quite confusing.

Please do not hesitate to correct my code, as I'm not very familiar with Rust.
For sanity check the csv output before and after my change is the same.

The parameters are therefore now:

Usage: unifiedlog_iterator [OPTIONS]

Options:
  -l, --live <LIVE>      Run on live system [default: false]
  -i, --input <INPUT>    Path to logarchive formatted directory [default: ]
  -o, --output <OUTPUT>  Path to output file. Any directories must already exist [default: ]
  -f, --format <FORMAT>  Output format. Options: csv, jsonl. Default is autodetect [default: auto]
  -a, --append           Append to output file If false, will overwrite output file
  -h, --help             Print help
  -V, --version          Print version

[puffyCid]

thanks!
I will try to review and merge this weekend

[puffyCid]

everything looks fine @cvandeplas. Only 2 small requests:

1. Please run cargo fmt on the unifiedlog_iterator example
2. Please run cargo clippy on the unifiedlog_iterator example and fix the very minor clippy issues

Thanks!

[cvandeplas]

I believe this should address the issues.
Note that there was one issue with the parser.rs that occurred when I merged with upstream. This commit also fixes that one.