Add decrlarations from ceval.h

Add PyEval_InitThreads and PyEval_ThreadsInitialized

Added an example of iteration for x in vector.

Closes #1771.

This reverts commit eb0e4666.

Fix importing of namespace packages. Add in a regtest for the same.

Fix warning about "comparison between signed and unsigned" in example and make it fully C89 compatible.

Updated runtests to exclude the pyximport_namespace test. Implicit namespace packages were introduced in Python 3.3.

Added tests for the convolve with the memoryviews in the docs.

Remove redundant helper function "__Pyx_ImportModule()" which was only needed in Py<2.6 when PyObject_GetAttrString() and PyImport_ImportModule() did not take const string arguments.

Mark several one-time functions (used during module init) with CYTHON_SMALL_CODE to reduce their binary code impact on the overall module size.

Avoid some overindentation in the generated C code due to duplicated opening braces inside of C macros.

Add tutorial on how to call C function with numpy arrays.

Corrected the description of a test option.

[Docs][Ready for Review] Added documentation on extension class instanciation from existing pointer