v0.9.0rc5

• Introduce new --diff-statements option (default off for now)
  • This calculates the diff for the counter values of pg_stat_statements on the client (i.e. collector),
    instead of the server for increased accuracy and protection against out-of-order processing
• Introduce "opts" to the snapshot, for indicating which options were chosen
• Never open more than 1 connection to the same database
  • This covers edge cases like sending a lot of SIGHUP signals
  • In case we detect more than 1 connection we error out and exit, to avoid
    clogging the database
• Use AWS EC2 instance role if no credentials are specified