Changed the numpy tutorial to make is faster to understand.

See #2529.

See #2529.

See #2529.

See #2529.

make the fast-call signature test compatible with Stackless Python

Move PyFrame localsplus offset calculation to a more appropriate utility file where it can be included conditionally.

make __Pyx_PyFunction_FastCallNoKw compatible with Stackless Python

Compute the offset of the PyFrameObject member "f_localsplus" at runtime,
because the layout of PyFrameObject differs between regular C-python and
Stackless Python.

DOC: use rst not md in for numpy debug error link

Add METH_STACKLESS to the bit mask used to test the call signature.

Also retry "apt-get update" in travis if "apt-get install" fails, because that was probably the reason.

Try to stabilise a test that depends on importing from the current directory right after creating a module there.

Adding tests for "pure python mode" part 13

Removing the reference guide from the docs.

Gradually enabling PEP8 checks on Travis ci.

Moved the Cythonize section in the userguide.