Improve command line option grouping and readability

Renamed command line options:

• -log → -log-file
• -summary-interval → -log-summary-interval
• -unsafe-logging → -log-unsafely
• -verbose → -log-verbosely

Deprecated options are still usable.
Whenever a deprecated option is used, a warning to the log/stderr is being
output to remind the operator/user to switch to the new option.

• Added deprecation info to the option descriptions of the --help page
• Slight correction of the option descriptions
• Updated --help page content in proxy's README.md