allow any leading timezone

[jtmoon79]

Currently

CLI options -u and -l will preprint the UTC or Local timezone. However, a user may want to review syslogs according to a different timezone.

Feature Request

Allow CLI option for any timezone to be preprinted. e.g.

   -pz, --prepend-timezone    Prepend DateTime in the passed Timezone for every line.
                              Accepts all strftime timezone formats.

extra TODOs

Update other CLI options.

   -u , --prepend-utc   Prepend DateTime in the UTC Timezone for every line. This is the same as passing "-pt UTC".
   -l , --prepend-local Prepend DateTime in the UTC Timezone for every line. This is the same as passing "-pt Local".

Add -pz to the same CLI option grouping.

Add example to README.md

            Print only the syslog lines that occurred two days ago during the noon hour in
            Bengaluru, India (timezone offset +05:30) but shown in timezone Bengaluru, India.

            ```lang-text
            s4 /var/log -pz "+05:30" -a "$(date -d "2 days ago 12:00" '+%Y-%m-%dT%H:%M:%S') +05:30" -b "$(date -d "2 days ago 13:00" '+%Y-%m-%dT%H:%M:%S') +05:30"
            ```

[jtmoon79]

Added in 630b8ce