Line editor

X Get crossterm working
X Line input
X Printing a prompt
X Raw input mode
X Backspace
X Exiting
X Arrow key input
X Left/right and inserting text
X Backspace from middle of buffer
X Deleting from middle of buffer
X Fixed the scroll-off-the-bottom issue
* Editing engine
  X Create the engine
  X Initial commands for the engine
  X Output commands from engine to the line editor
* UTF-8 support
  X Line buffer
  X Backspace/delete
  X Navigation
  X Unicode w/ joiner support for removal
  * Multiline editing
X History
X Up/down history
X Home/end
X Refactor keypresses to flush at the end
X Ctrl-A, Ctrl-K, etc
X More Ctrl-??? key combinations
X "engine"?
X Command pattern
X Split off lib
* Split Engine into its isolated parts
  * History
  * Maybe cut buffer. Question: do we want to connect to the OS's clipboard?
* Validation
* Autocompletion
* Make Prompt trait and make prompt configurable
* Multiline support
* Syntax highlighting
* Under status
* Hinting
* vi mode
* Async/parallel prompt
