Fix: absolute import handling

Do not install test dependencies on CPython dev versions in travis as they are likely to fail in pre-releases.

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

Fix support for functions with ndarray parameters of type npy_bool

Fix stop generating code that compiler skips

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 warn.undeclared #2685

fix co_firstlineno for functions that have decorators

Remove support for Py2.6 and various quirks that special-cased it

Closes #2692.

Fix: Exponentiation of integer constants

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