rmd_reader: Make set_initoptions() compatible with rpy2 v3

[stephenfeagin]

Fixes #1132.

rpy2 changed its API for 3.0, and moved set_initoptions() from rpy2.rinterface to rpy2.rinterface_lib.embedded. It also changed the argument from a tuple of bytes to a tuple of strings. This PR tries to run it as rpy2 v2, and if the method lookup fails, it tries the rpy2 v3 setup. I've tested this with both rpy2==3.0.2 and rpy2==2.9.5.

[jranke]

I just upgraded to the upcoming Debian bullseye, and rpy2 v2 does not install any more. First I deinstalled the current Debian package of python3-rpy2 3.4.2. Then pip install "rpy2<3" fails with (only giving the most relevant part of the output):

...

 ./rpy/rinterface/_rpy_device.c: In function ‘_GrDev_close’:
    ./rpy/rinterface/_rpy_device.c:175:7: error: ‘_Py_DEC_REFTOTAL’ undeclared (first use in this function); did you mean ‘_Py_DECREF’?

...

For me this means that I would really like to see rmd_reader to be compatible with current rpy2, which is the purpose of this PR. Note that the README should be updated as well, as it currently says that rpy2 v2 is needed and recommends the abovementioned pip install command.

[jranke]

Ah, yes, and I I can confirm that the PR solves the problem. I checked out the PR and rebased it on master. Should I update the Readme and requirements.txt and create a new PR, or what would be your preferred procedure here?

[justinmayer]

@jranke: Thank you for reminding me about this. I think the best thing to do here is to merge this PR, after which you can submit a new PR to address the other points you raised (README, requirements.txt, etc.).

@stephane-caron: Very sorry for the delay in merging your contribution, which is much appreciated! 😅