Provide time.Ticker, time.Timer and friends that can be used directly
from C++ and Pyx/nogil codes. Python-level classes become small wrapper
around pyx/nogil ones.

This is the first patch that moves to Pyx/nogil classes that are
dynamically allocated on heap. refptr<T> is used to automatically manage
lifetime of such objects. At Pyx level exposed API is very similar to
Python-one, while internally it uses refptr<T> and friends.