Support `package_config.json` files.

This version retains the original API and adds a completely new API for working with package_config.json files.

The original API will be removed in version 2.0.0.

Support extended .packages format

1.1.0

Make version number ready for release.

1.0.4

1.0.4

• Set max SDK version to <3.0.0.

1.0.1

Merge pull request #41 from dart-lang/pq-patch-1

Update SDK constraint to be 2.0.0 dev friendly.

0.1.5

`0.1.5` CHANGELOG update pre-publish.

Adds:
* FilePackagesDirectoryPackages.getBase(..)` performance improvements.

BUG=
R=scheglov@google.com

Review URL: https://codereview.chromium.org//2051143002 .

0.1.3

Update version number before publishing.

BUG=

Review URL: https://codereview.chromium.org/1301443005 .

0.1.3-dev

Merge pull request #31 from dart-lang/parse_test_fix

Invalid test cleanup (parse_test) [TBR].

0.1.1

Merge pull request #26 from dart-lang/v_bump

Version bump.

0.0.3+1

Remove dependency on http package

0.0.3

Separate out VM dependencies.
The Packages interface class should not depend on a platform specific
library (dart:io).
This removed the dependency, and also splits the implementation
classes into those that are generally applicable and those that
requite dart:io to operate (the "local packages directory" which
allows iterating the package names by scanning the directory).