Parse redis-uri at CLI, and allow for redis AUTH

  - Allow for authentication to a Redis server that is protected by a
password.
  - Adds `-redis-uri=` CLI argument for specifying the redis connection
    information in standard URI notation.  This is the default assumed
by many
    12-factor apps. The implementation here will also use Redis
defaults for
    any fields not specified by the user (port, db number).
  - If no redis information is specified, use default case (e.g.
    `redis://localhost:6379/0`)
  - Check for connection error when first creating Redis connection
pool at
    startup -- if found, inform user and die gracefully.
Merge branch 'redisuri' of https://github.com/mroth/forgettable