Create general-purpose terminal emulator base classes

[oubiwann]

Part of epic:

• A debug REPL for signal processing #21

Tasks:

• Stub out library and UI files (.svg, .cpp, .hpp files)
• Create Shell header for implementation:
  • read
  • eval
  • print
  • loop
• Create Shell no-ops for testing:
  • read (no parsing)
  • eval (echo)
  • print
  • loop
• Allow for defining welcome, prompt, and banner
• Get primitive read-print capability in a text area
• Store entries as vec of strings
  • maintain a vec for display purposes
  • maintain another vec for the complete session history
• Emulate terminal behaviour
  • only read when last line is change
  • don't make changes to text area if not made in last line
  • don't go past max height
  • when max height is reached, pop off first element from display vec to make room
  • don't allow edits in the prompt area
  • add readline suppport
• Reset button for clearing history and memory
• Add support for slurping files (definitions)
• Add support for dumping command history to file
• Provide a means of setting specific shells
• Maintain cross-restart command history (module json file?)

Blocks:

• Create a system shell module #26
• Create REPL module for ft-lisp #24

[oubiwann]

Responding to arrow keys might be a nice first step at emulating readline. Ideas here:

• https://github.com/Dewb/monome-rack/blob/main/src/teletype/screen/TeletypeScreenWidget.cpp