For polar plots the (unsightly, and unhelpful) r-axis is hidden by default, instead of the grid being enabled by default.

This PR handles rticks(), rtickformat(), rticklabels() and rtickangle() to generate the corresponding gnuplot commands even when the r-axis is hidden.

Additionally, it handles `rticks({})` and `rticklabels({})` properly by essentially setting `rtickformat("")`. This ensures that labels are hidden without having to disable the grid.

fix #376

fix #393

* Set errno for popen and pclose for WIN32 just like POSIX does
(at least mingw64+wine seems to decode the error message without doing anything extra)

* A work around for popen/pclose: complicated but works

* Refactored popen/pclose into custom implementation and added c++ wrappers

* Removed exceptions and cleaned up process pipe api

* Refactored popen/pclose into C++ class

* Fixed trivial issues for Linux

* Simplified the move semantics by avoiding virtual functions

* Moved error reporting into common_pipe

* Simplified open and close in case the pipe is already opened/closed

* Fixed error handling for MSVC, which very weird:
MSVC rejects strerror, suggest to use "secure" strerror_s, but then does not supply strerrorlen_s
GCC does not provide strerror_s, looks like strerror is good enough there.

* MSVC is not following any standards