Corrected broken URL of the notebook.

ignored the build of the docs in git.

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.