v0.6.0

Documentation improvements:

• Rewrite the batch-driven Streamer README example to stay true to its purpose and
  reflect closer the real world scenarios it is meant to serve in (TODO);
• Refactor internal benchmark package as a stand-alone binary,
  and rename it to integration:
  • The latter because it was from the beginning used
    as integration dev-triggered tests rather than a true benchmark;
  • And the first to allow more flexibility and differentiation in how we test what streamer configuration;
• Add developer instructions to the README;

Bug Fixes:

• Storage Streamer Client couldn't be closed without hanging, now it can be closed;
• Storage Streamer Client can now be used with BigQuery.Schema, previously it would result in a schema name error;
• Storage Streamer Client now demoted Canceled/Unavailable code errors for append rows to debug logs: as these are related
  to underlying connections being reset or a similar kind of EOF event;
• improve & clean up integration tests;