v0.6.2

Major Changes

• #79 Added command system, and rewrote menu and toolbar modules. Commands are now defined
  by deriving from CommandDefinition, and command handlers implement ICommandHandler.
  Menu items and toolbar items no longer define their own handlers; instead, they reference
  the command definition. New command routing logic chooses the appropriate command handler,
  depending on context. This system is built on top of WPF's command system, but extends
  it in useful ways.
• Reworked themes. There are now 3 built-in themes: Light, Dark, and Blue. You can use
  IThemeManager to programmatically change theme, or use the combobox in Tools / Options.

New Features

• #58 Upgraded to Caliburn Micro 2 (Kris Janssen)
• #52 Add DataTemplateSelectors to GraphControl (KingKnecht)

Resolved Issues

• #54 Overhaulted saving document state (Tristyn Stimpson)