Docs: Undo PR #2439 because readthedocs does not behave as expected.

The change of making "tstate->exc_state" a struct was introduced in CPython 3.7.0a3 and not 3.7.0a2, which some people still seem to be using right now.

Simplified the first example of fused types.

Changed the organisation of prange.

Moved the cythonize description from the docs to the docstring.

See #2180.

Enable automatic redirect for outdated pages in the docs.

Docs: Fixed a typo in a filename causing it not to be displayed in the docs.

Changed some URLs to fix some links redirection.

Fixing some broken links.

Added tests for "language basics" part 5

Adding tests for "sharing declarations" part 1

Repair accidentally broken support for comparing non-trivial objects (e.g. NumPy arrays) to integer constants.
Closes #2444.

Added support for C++11's <forward_list>.

Added a note on the compilation with numpy to avoid confusion.

Added tests for "language basics" part 2