build_barback 0.1.0

Updated to reflect the new support for reading/writing as bytes in the build
package, and the removal of the Asset class.

New Features

• BuilderTransformer now supports wrapping transformers that read or write
  their inputs as bytes.
• The Resolver implementation now has isLibrary to check whether an Asset is a
  Library and throws an exception rather than returns null on getLibrary when
  it isn't

Breaking Changes

• Stopped exporting lib/src/util/barback.dart which contains internal only
  utilities. Specifically, the following items are no longer public (some are
  deleted entirely or had breaking changes as well):
  • toBarbackAsset
  • toBarbackAssetId
  • toBarbackTransform
  • toBuildAsset
  • toBuildAssetId
  • toTransformLogger
  • BuildStepTransform