List all the pyind11 exception and refer to code.

I wanted to know excacly what existed, because I wanted to raise a
`RuntimeError`. In practice, it took me quite some time to find where
(a) the pybind11 exceptions are defined, (b) how the C++ exceptions
are converted to Python ones.

At the end, I discovered everything else is converted to RuntimeError,
so I do not need to do anything.

The link is a result to github search, which may be more robust to
moving code around.

s#

Author: jblespiau

docs/advanced/exceptions.rst

@@ -60,7 +60,7 @@ at its exception handler.
 +--------------------------------------+--------------------------------------+
 | :class:`pybind11::buffer_error`      | ``BufferError``                      |
 +--------------------------------------+--------------------------------------+
-| :class:`pybind11::import_error`      | ``import_error`                      |
+| :class:`pybind11::import_error`      | ``import_error``                     |
 +--------------------------------------+--------------------------------------+
 | Any other exception                  | ``RuntimeError``                     |
 +--------------------------------------+--------------------------------------+