to do
/////

* Write importlib.__import__

* Document
    + Package.
    + import_module
    + __import__

* Create reasonable base tests that all finders and loaders must pass so
  that various implementations can just subclass as needed.

* Expose built-in and frozen importers.
    + Make staticmethods so that class can be used directly.

* Reorganize support code.
    + Separate general support code and importer-specific (e.g. source) support
      code.
        - Create support modules for each subdirectory (as needed).
    + Add a file loader mock that returns monotonically increasing mtime.
        - Use in source/test_reload.
        - Use in source/test_load_module_mixed.

* API simplification?
    + read_source -> get_data/source_path
    + read_bytecode -> get_data/bytecode_path
    + write_bytecode -> complete set of bytes for bytecode instead of
      individual arguments.

* Implement PEP 302 protocol for loaders (should just be a matter of testing).
    + Built-in.
    + Frozen.
    + Extension.
    + Source/bytecode.

* Create meta_path importer for sys.path.

* OPTIMIZE!
  + Write benchmark suite.
  + Fast path common cases.
    - Absolute name from sys.path.
    - Relative name from sys.path.

* Public API (w/ docs!)
  + abc
      - Finder
        * find_module
      - Loader
        * load_module
      - ResourceLoader(Loader)
        * get_data
      - InspectLoader(Loader)
        * is_package
        * get_code
        * get_source
      - (?) SourceLoader(ResourceLoader)
        * source_path
        * bytecode_path
        * write_bytecode
  + util
      - get_module decorator (new name)
      - check_name decorator (new name)
  + hooks (?)
      - (?) Chained path hook/finder
      - BuiltinImporter
      - FrozenImporter
      - (?) FileFinder
      - Extensions importers
          * ExtensionFinder
          * (?) Loader
      - Source/bytecode importers
          * SourceFinder
          * (?) Loader
  + __init__
      - __import__
      - import_module (backport to 2.7)
      - resolve_name (backport to 2.7)

* Bootstrap importlib as implementation of builtins.__import__