call-outs to existing software

# call-outs to existing software
components with `$` as the first character in their name are converted to shell-outs
https://cdn.kinopio.club/QARFKBLa_WOFzbeGPkOxk/Screenshot-2023-10-15-at-9.18.46-AM.png
in this case, `$m4` invokes the `m4` command and gives it `stdin` from the input pin `input`
this is "inefficient" for production software but is reasonable for development tools
`stdout` and `stderr` are collected and sent to the appropriate output pins (`output` and `error`)
back https://kinopio.club/software-simplification-compendium-ivD_Z4-xQN4ZlluzLbo_R

# call-outs to existing software
components with `$` as the first character in their name are converted to shell-outs
https://cdn.kinopio.club/QARFKBLa_WOFzbeGPkOxk/Screenshot-2023-10-15-at-9.18.46-AM.png
in this case, `$m4` invokes the `m4` command and gives it `stdin` from the input pin `input`
this is "inefficient" for production software but is reasonable for development tools
`stdout` and `stderr` are collected and sent to the appropriate output pins (`output` and `error`)
back https://kinopio.club/software-simplification-compendium-ivD_Z4-xQN4ZlluzLbo_R