hide log messages by default

• Re-enable log messages with -v option
• See: #7

Send log messages to stderr

• Allow the wrapped commands to pipe as normal, by routing any logging to stderr instead of stdout

Provide optional credentials duration

• Allow the user to provide an optional credentials duration between renewals (export VAULT_CREDENTIALS_DURATION)
• Default credentials duration is set to 1 hour.

Bug Fix and Improvements

• BugFix: use GNU compliant date format
• Show release version in the debug output
• Track changes between releases