Moves config validation to own functions to enable tools to use them
Moves sharding config to enum
Makes defaults public
Make connect_timeout on pool and option which is overwritten by general connect_timeout
* constants
* server.rs docs
* client.rs comments
* dead code; comments
* comment
* query cancellation comments
* remove unnecessary cast
* move db setup up one step
* query cancellation test
* new line; good night