clickhouse-go compatible DSN

[yuzhichang]

clickhouse-go DSN:

• alt_hosts - comma separated list of single address host for load-balancing
• connection_open_strategy - random/in_order (default random).

These parameters enables load-balance and fault- toleration.

[zhicwu]

In general all clients should use similar settings as in official clickhouse-client, and behave in the same way. It's a good suggestion and we'll revisit this in 0.4.

[zhicwu]

Not going to use the exact same DSN, because Java client and JDBC driver support multiple formats(TSV and RowBinary) and protocols(http, https, grpc, tcp and tcp secure) as of 0.3.2. It's more natural to use nested URLs as mentioned in #894.