A running process. The three type parameters provide the type of the
standard input, standard output, and standard error streams.
To interact with a Process use the functions from the section
Interact with a process.
Use OS processes just like native Haskell functions - to generate,
transform or consume streams.
See Streamly.System.Command module for a higher level wrapper
over this module.
See also: Streamly.Internal.System.Process for unreleased
functions.