Add "generator_stop" to default future imports for language_level=3

Support for "volatile" keyword

See #2580.

Add a link to the "limitation" docs page that selects the known differences in Python semantics from the Github issue tracker.

Accessing the first element of a `std::vector` that is empty results in
a crash.

Fix crash in lvalue_refs test.

Accessing the first element of a `std::vector` that is empty results in
a crash.

De-optimise the unicode methods ".upper()", ".lower()" and ".title()" on single character values since they must still be able to return multiple characters.

The __PYX_XDEC_MEMVIEW statements generated for try/finally statements
varied per build if there were multiple types of variables to be cleaned
up.

Fix source of non-deterministic cython output for try/finally statements

The __PYX_XDEC_MEMVIEW statements generated for try/finally statements
varied per build if there were multiple types of variables to be cleaned
up.

"convolve_cy.so" -> "compute_cy.so" to match imports used in this tutorial.

This fixes the following compiler warning:
  warning: cast discards ‘const’ qualifier from pointer target type [-Wcast-qual]

fix the comments to have a  c89 compliant generated code

TypeConversion: Fix pointer qualifier compiler warning [-Wcast-qual]

Only generate __qualname__ in Python versions supporting it

This fixes the following compiler warning:
  warning: cast discards ‘const’ qualifier from pointer target type [-Wcast-qual]

Speed up attribute lookups that do not care about the AttributeError

Add a new utility function "__Pyx_PyObject_GetAttrStrNoError()" that does not raise AttributeError if the lookup fails, and use "_PyObject_GenericGetAttrWithDict()" for it in Py3.7+ to avoid instantiating the exception completely.

DOC: Fixed name of .so file in userguide's numpy_tutorial.

"convolve_cy.so" -> "compute_cy.so" to match imports used in this tutorial.