subProcessF :: String -> F String (String ⊕ String)
subProcessF allows you to start a subprocesses and communicate with it. The subprocess
can execute any shell command, so
subProcessF opens up the possibility plug in
arbitrary external software in a fudget program.
Left strwhen the subprocess puts
strin its standard output stream.
Right strwhen the subprocess puts
strin its standard error stream.
cmd :: String
Stdio communication: stdioF et al.
subProcessF was inspired by the C function