Reorganize barback's source files.

This creates four directories beneath barback/lib/src:

* asset/ contains the Asset and AssetNode classes, as well as various
  classes for dealing with them.

* graph/ contains the classes that make up the barback asset graph, as
  well as utility classes that are specific to these (such as
  NodeStreams).

* transformer/ contains Transformer and similar classes (such as
  TransformerGroup), as well as the classes (such as Transform) that
  are passed to Transformer methods.

* utils/ contains utility classes that aren't barback-specific (such
  as CancelableFuture).

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//261823008

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@35777 260f80e4-7a28-3924-810f-c04153c831b5
45 files changed
tree: 3471e9a88b88e3cf322b6d0ef94d7ae45b46a0cc
  1. example/
  2. lib/
  3. test/
  4. CHANGELOG.md
  5. LICENSE
  6. pubspec.yaml
  7. README.md
README.md

Barback is an asset build system. It is the library underlying pub's asset transformers in pub build and pub serve.

Given a set of input files and a set of transformations (think compilers, preprocessors and the like), it will automatically apply the appropriate transforms and generate output files. When inputs are modified, it automatically runs the transforms that are affected.

To learn more, see here.