Get rid of ESS dependency

[meedstrom]

I'd like to avoid this heavy dependency. ESS can be complicated to get functional, like the other pre-melpa behemoths org-mode, pdf-tools and auctex.

My problems with running R/Rscript with vanilla make-process &c:

• [ ] text encoding issues
• [ ] directing output to the right place
• [ ] comint escape codes all over the output
• [ ] how to keep a running process and send more code to it like with =ess-execute=?