v0.5.1

Update storage API documentation & end-to-end tests:

• storage writer API expects proto2 semantics, proto3 shouldn't be used (yet);
• the normalizeDescriptor
  should be used to get a descriptor with nested types in order to have it work nicely with nested types;
• The proto well-known types aren't yet properly supported,
  and Timestamp is among them. The public docs have a section on wire format conversions:
  https://cloud.google.com/bigquery/docs/write-api#data_type_conversions.
  • Short answer: use an int64 with epoch-micros for fields that have the Timestamp type...
    and this instead of import "google/protobuf/timestamp.proto";
• Batch client supports auto-detection of BigQuery schema for CSV and Json source formats,
  with Json you have to be aware in that case however that you match the casing exactly,
  as otherwise it will complain about duplicate case-insensitive fields, go figure...

Bug Fixes:

• a couple of error logs used wrongfully the directive %w for errors instead of %v,
  this has now been corrected and should result in cleaner logs;