better connection emulation and more options

• You can establish a connection without selecting a database.
  This is useful when you want to create the database using this api (eg with the doctrine:database:create command).
  It is also now possible to switch databases using use dbname; which won't result in an actual query but will internally set the database name in the connection instance. $driver->getDatabase($connection) will also correctly report the database in that case.
• You can now make any query block until the database is available if it was paused.
  There are 2 new options for that: pauseRetries and pauseRetryDelay. You can read more about them in the readme.
  I'll continue to default to an error instead of blocking as waiting for a minute is usually not a good idea. Lambda events will automatically retry after a minute (using exponential backoff) so you normally don't have to worry about it and interactive page loads will always feel broken if the database is paused so you'll need a better handling in that case.
• I removed the direct dependency on guzzle by setting options though the aws-sdk.
  You still need guzzle, it's just not my dependency anymore. There is an experimental branch which uses async-aws but that sdk may need some additional testing work for which I'm currently not motivated and don't have the time.