Add export of the bytearray cpython api

Fix usage of special name "sizeof" in a test: cannot be assigned to a variable because it is not an actual function.

See #2559.

Set the maximum line length to 150.

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.