Use atom.commands for commands
Handle preview:file command with atom.commands

It’s matched against specific selectors in the tree view.
Use config schema
:lipstick:
Use Workspace::addOpener
Use onDidActivateAll
Use atom.commands to subscribe to view-local commands
Fix deprecated method calls and event subscriptions
Use Config::onDidChange
Fix context menu format
Use File::onDidChange
Use CompositeDisposable instead of Subscriber mixin
Remove WorkspaceView references
Use atom-space-pen-views instead of deprecated exports from atom module
Use atom.grammars instead of atom.syntax
Eliminate pane item event deprecation warnings
Deprecate markdown-preview:markdown-changed jQuery event

Provide an ::onDidChangeMarkdown method as a more explicit alternative.
Avoid deprecation warnings for custom event

Subscribing to it is deprecated, but I wanted to keep the noise out of
the specs in the meantime.
Remove use of deprecated Config::toggle
Merge pull request #161 from atom/ns-modernize

Remove usage of deprecated APIs