[feature/spawning-VM] Add a feature that spawns an outer Elixir by Port to the HtPipe.htp function with Node communication

[Susumu Yamazaki]

• Redefine HtPipe.htp/2 with adding a parameter of a keyword list for describing options.

• Add an option for timeout.

• Add an option for spawning a light-weight Elixir process with Task.Supervisor or a OS-level process with Port and Node, which is the adding new feature.

• Implement the new feature.

• Describe tests to evaluate robustness for the both spawning policies.