initial commit: common layout
basic input, editing and stack operations
project rename
operations and stack
op keys and auto-push
more robust push_op()
put operations into stack config
execute button
type operations args
correct pop_op()
operations priority fix
switch sign and point buttons
raise OperationError on op args type mismatch
catch and report OperationError
placeholder texts
StackError is raised on stack errors
catch and show stack errors
stack view is scrollable
remember stack textview, not textbuffer
cursor reset on sign change