Closes #1635.

Update URLs to https:// in docs and comments

Export "PyInit___init__" and "init__init__" as additional module init functions under Windows to make compiled packages work.

Avoid const-ness compiler warning in __Pyx_PyObject_AsWritableString

Run stackless builds in travis before the pypy builds (which take very long), and require them to work, now that they seem to succeed.

Try Mapping protocol before Sequence protocol on getitem/setitem/delitem

Correctly remove future_directives with # cython: language_level=2

Use the same list of potential package init file names everywhere

Use the same list of potential package init file names everywhere (not just "__init__.py" but also .pxd and .pyx).
Closes #2665.

Replace MD5 file hashing by SHA-1, both because it's faster (by 25% on 64 bit Linux) and because MD5 is no longer allowed in US FIPS 140-2 environments.
Closes #2790.

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

Support for "volatile" keyword

See #2580.

Try the Mapping protocol before the Sequence protocol on getitem/setitem/delitem since that is the order that Python uses.
Closes #1807.

This avoids the compiler warning
  warning: cast discards ‘const’ qualifier from pointer target type [-Wcast-qual]
by casting the pointer to uintptr_t before removing the const-ness.

The warning was introduced in 6cd70f09

Also merge the two places that define stdint types.

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.