Cleanup windows.dart code.

- windows events now use Dart streams
- added unit tests for all windows methods
Uncomment lines I accidentally left commented out in the last commit.
Commit unsaved changes.
context_menus.dart cleanup and tests.
Extend documentation on classes.

Changed ContextMenuClickEvent.mediaType's type to ContextMenuContext.
Merge pull request #61 from DrMarcII/master

Improvements to chrome.windows APIs and tests
Merge pull request #62 from DrMarcII/master

chrome.contextMenus cleanup and tests
Minor cleanup of extension API files.
Adding Marc Fisher to readme.
Merge pull request #63 from DrMarcII/master

Minor cleanup of extension API files.
Lots of code cleanup.

Cleanup runtime.dart.

Fixes to ChromeCompleter.

Comment out test chrome.app.window.minimize test that is not completing on
my system.

Other cleanup related to changes to runtime.dart and chromecompleter.
Uncomment lines that I accidentally left commented out.
Merge branch 'runtime'
Edits in response to pull request comments.
Merge pull request #64 from DrMarcII/master

Fixes to (primarily) runtime.dart.