Log Message:
tex-mathtools: update to 1.29

* In section `Special mathtools options` clearified when `gathered` of pure
amsmath might give a warning.
* Added 3.6 note 3: about \section{foo $\norm[\big]{bar}$}.
* Renamed a few colon combo symbols and added a few extra for completeness.
  A package option is available to revert the change.
* Added a warning if mathtools is loaded *after* `unicode-math`

Please note that this is a **breaking** change! For many years mathtools have
provided some colon related symbols, like :=. The names of which was copied from
txfonts/pxfonts. It turned out that these names were inconsistent, for example
\coloneq would be :- where as \coloneqq would be :=. This has now been changes
such that both provides :=. Additional colon symbols have also been added. If
needed, the package option legacycolonsymbols will revert the old behaviour of
\coloneq, \Coloneq, \eqcolon and \Eqcolon.