Consider adding Cython bindings

[vyasr]

Currently rapids-logger is a pure C++ library. However, some consumers of it expect to also be able to expose its bindings in Python. Currently that is the case for both rmm and cuml. As of the writing of this issue, we determined that the extra packaging work that would need to be done to create Python packages of rapids-logger that expose the relevant bindings is more work than it's worth, so rmm and cuml are simply going to write their own small set of Cython bindings to the C++ loggers, which means they will be doing some cdef externs from rapids-logger headers directly. If at some point it becomes clear that the benefits outweigh the costs (i.e. if more projects start needing these bindings we can reconsider adding a minimal rapids-logger Python package to centralize and export those bindings.