release 1.09.6

release 1.09.6

- all key aliases moved to module DCT::Bindings
- number of menu items depends on screen width
- hooks allowing for extra code at reload, showentry, and precmd
- all menu related functions moved to menu.pm
- unit conversion out of main program (entirely into unitconv.pm)
- backspace becomes "back" (soft drop, like old "drop")
- normal drop command (alt+bs) removes input/stack value at once
- $val{frac} default undefined instead of 0