Add ::addLeftItem and ::addRightItem

Signed-off-by: Nathan Sobo <nathan@github.com>
Place items further in when no priority is given

Signed-off-by: Nathan Sobo <nathan@github.com>
Use new APIs for adding built-in items

Signed-off-by: Nathan Sobo <nathan@github.com>
Allow status bar items to be removed
Make status-bar API more like panel API

Signed-off-by: Nathan Sobo <nathan@github.com>
Deprecate old status bar APIs
:lipstick:
Merge pull request #45 from atom/mb-panel-like-api

Give status bar a panel-like API