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.

Fix Memviewslice docstrings & Test

[#2634] Merge Fix 

Workaround for long internals misconfiguration on 64-bit MinGW.

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

Fix reimport_from_subinterpreter test when PYTHONPATH is set