add SRFI 197 (pipeline operators)

[sam-d]

adapted the reference implementation of SRFI 197 from here: https://github.com/scheme-requests-for-implementation/srfi-197/ originally developed here: https://github.com/ar-nelson/srfi-197

This code is thus licensed under MIT license and copyright (c) Adam Nelson with minor edits by myself to make it work with chez-scheme

[arcfide]

Thanks for this! Do you think you could include a license file and/or license information in the files to make sure we preserve that copyright information?

[sam-d]

Done!

[arcfide]

Great, thanks!