[docs] lack of PyExc_BufferError doc (issue 19225)

[vadmium+py at gmail.com]

https://bugs.python.org/review/19225/diff/16404/Doc/c-api/exceptions.rst
File Doc/c-api/exceptions.rst (right):

https://bugs.python.org/review/19225/diff/16404/Doc/c-api/exceptions.rst#newcode829
Doc/c-api/exceptions.rst:829: | :c:data:`PyExc_UnBoundLocalError`      
| :exc:`UnboundLocalError`        |          |
Lowercase B

https://bugs.python.org/review/19225/diff/16404/Doc/c-api/exceptions.rst#newcode885
Doc/c-api/exceptions.rst:885: These aliases used to be separate
exception types.
I think it might be better to keep the versionchanged close to the table
of aliases, and then the notes. The version changed only applies to the
aliases, but the notes apply to both tables.

https://bugs.python.org/review/19225/diff/16404/Doc/c-api/exceptions.rst#newcode933
Doc/c-api/exceptions.rst:933: single: PyExc_BufferError
IMO these index entries should go _before_ the appropriate table, not
after. But I guess that is a separate problem.

https://bugs.python.org/review/19225/