v0.2.0

Basic edition features and commands are now available:

• insert characters in insert mode with support for Enter/Backspace
• d deletes a line
• x deletes the current character
• o inserts a newline after the current line and switches to insert mode
• O inserts a newline before the current line and switches to insert mode

A lot of work went into implementing a Console trait, both implemented by the Terminal struct, as well as a MockConsole one, and passing it around the Editor, so that we can mock the terminal itself, to unit test the editor.