Closes #2671.

Closes #2729.

Plus Start filling unit test cases

“It have”-> “it has”
“Parralelism” -> “parallelism”

Also add a compile time check for SIZEOF_VOID_P.

This fixes #2670.

See also
https://bugs.python.org/issue35037
https://bugs.python.org/issue4709

gh2638 absolute import handling

This change was actually unnesarry as with the new regex we iterate
over all possible combinations of package and modules.

The types of variables __pyx_PickleError, __pyx_result from generated
unpickle function, and variables state, _dict from __reduce_cython__
generated method were not declared.
So warnings were raised with warn.undeclared for every single extension
type.

Now, we define the type of these variables, and no warnings are raised.