Crate extendr_engine

A sigleton instance of the R interpreter.

Only call this from main() if you want to run stand-alone.

Its principal use is for testing.

See https://github.com/wch/r-source/blob/trunk/src/unix/Rembedded.c

Functions

end_r	Close down the R interpreter. Note you won't be able to Restart it, so use with care or not at all.
start_r