[docs] [issue26535] Minor typo in the docs for struct.unpack

[Martin Panter]

Martin Panter added the comment:

Here is a new patch:

* Use “The buffer’s size in bytes” wording
* Avoid brackets inside brackets
* Fix the three unpack functions and corresponding methods
* Also fix doc strings

----------
stage: needs patch -> patch review

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue26535>
_______________________________________