Drop the TODO.md section numbers from 26 files

Eighty-five comments cited section numbers -- 1.1, 2.2.6, 3.6 -- from a
numbering the file had already abandoned before the move to the tracker. They
label completed work, so the pointer was the only wrong part.

The citation is removed and the sentence kept, which is what issue #27
recommended: these are labels, not references, and a label carrying a
version-dependent pointer goes stale again at the next reorganisation. Where a
pointer earns its place it names what actually holds the content now --
UPGRADING.md for the confirmed defects, libakerror #15 for the target
namespacing, issue #7 for the mutation survivors.

README.md and akstdlib.h sent readers to TODO.md for 'what is still open';
they name the tracker.

Verified: cmake --build build && ctest --test-dir build, 19/19.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-Authored-By: Andrew Kesterson <andrew@aklabs.net>

README.md

@@ -8,7 +8,8 @@ through [libakerror](https://source.starfort.tech/andrew/libakerror)'s
 and `errno`. It also provides data structures built on the same convention.
 
 Every entry point returns `akerr_ErrorContext *` and is marked `AKERR_NOIGNORE`.
-See `TODO.md` for the current state of the library and `UPGRADING.md` if you are
+Outstanding work is in [the issue tracker](https://source.starfort.tech/andrew/libakstdlib/issues).
+See `TODO.md` for where the library stands and what is deliberately not wrapped, and `UPGRADING.md` if you are
 coming from 0.1.0, which this release breaks.
 
 ## What it wraps