Check result of "declare_builtin()" because it might a) not have been found and b) not actually be a builtin. In both cases, it's actually not a literal.

Change annotation typing directive to cover all type annotations and modify annotation parsing to be more PEP 484 compatible.
Only "cython.*" types are interpreted as C types from now on, everything else is considered Python types for maximum compatibility with Python type hints.

Also parses variable annotations as type declarations.
Closes #1850.

Better fix for #1836: set frame flags to make CPython create a new dict for "frame.f_locals" at need.

Evaluate and join more f-string constants at compile time, including unprefixed strings.
Fix a case where f-string constants could have incorrect constant compile time result values, thus leading to incorrect comparisons and constant folding errors.

Implement two more special cases in fstring joining to reduce the need for runtime character size detection.

Move exception state cleanup into generator body code to allow a distinction between normal yields and yields in except blocks. They require different handling according to what CPython does.

Avoid some unnecessary strlen() calls in exception text formatting, while still keeping up the nice property of sharing const C message strings.

Specialise coercion from bytes to char* (and friends) to avoid going through several type checks in the generic "__Pyx_PyObject_AsStringAndSize()" function.

Closes #1791.

repair scoped comprehensions inside of generators and async functions by allowing their loop variables to be added to closures when necessary

refactor "yield from" and "await" nodes a little to provide a cleaner split between them (await nodes are not yield-from nodes)

repair comparison between C complex types and extension types: previously generated an invalid type check

This fixes #1752.

When the user asked for it (thanks to the --np-pythran flag), use
Pythran's Numpy implementation as a backend for numpy operation. This
flag forces the C++ mode, as the Pythran implementation is written in
C++. Distutils integration through the 'np_pythran' flag of the
cythonize API is also provided.

This commit also adds a Pythran mode for the tests, that can enable the
pythran mode for the C++ tests, and allows the reuse of Cython tests to
test for the Pythran integration.

When not imported, this caused was a runtime NameError.  Now an error
is given at compile time.