Closes #2134.

Added %%cython options.

Patch to add front() and back(), as per issue #2123.

Copy also the short long_neg() code from CPython for the specialised "abs(PyLong)" implementation to avoid jumping through call pointer indirections.

Added argument list for pyximport.

Apply the switch-transformation also recursively to if-clauses and else-body of if-statements that were converted.

Allow `NULL` to be coerced to a pointer to a fused type

Removed dead link to Cython bug tracker.

Cython numpy users

Changed the wiki url.

COMPAT: From the next release PyPy fixed tp_basicsize of PyType_Type

Closes #2152.