Add flag to expose removed files listing currently exposed by default

[atc0005]

Command and output from some work today to cleanup the /var/log/usage path on a server I'm helping to maintain:

$ sudo ./elbow-v0.7.15-0-g8844f4d-linux-amd64 --use-syslog --paths /var/log/usage/ --age 90 --remove
INFO[0000] Syslog logging requested, attempting to enable it  line=129 use_syslog=true
INFO[0000] Connected to syslog socket
INFO[0000] Starting evaluation of paths list             extensions="[]" file_age=90 file_age_threshold="2021-07-20T16:15:54-05:00" file_pattern= paths="[/var/log/usage/]"
INFO[0000] Beginning processing of path "/var/log/usage/" (1 of 1)  ignore_errors=false iteration=1 total_paths=1
INFO[0000] 2879 files eligible for removal (4.5 GiB)     extensions="[]" file_age=90 file_age_threshold="2021-07-20T16:15:54-05:00" file_pattern= iteration=1 path=/var/log/usage/ total_file_size=4796149148
INFO[0000] 0 files to keep as requested                  iteration=1 keep_oldest=false
INFO[0000] Ignoring file removal errors: false
INFO[0003] 2879 files successfully removed (4.5 GiB)

...

INFO[0003] 0 files failed to remove (0 B)
INFO[0003] Ending processing of path "/var/log/usage/" (1 of 1)  ignore_errors=false iteration=1 total_paths=1
INFO[0003] Elbow successfully completed.                 eligible_remove=2879 eligible_size="4.5 GiB" failed_removed=0 failed_size="0 B" success_removed=2879 success_size="4.5 GiB"

The ... line represents nearly 3,000 files removed and listed in the output. This should probably be hidden by default, but exposed when explicitly requested. Perhaps --list-removed-files or --show-removed.