This patch improves the documentation by completing the description of
the remaining so far undocumented OpenMP Memory-Management Routines
(except for the two function added in TR11, which are also unimplmeneted).
Current online version:

https://gcc.gnu.org/onlinedocs/libgomp/Memory-Management-Routines.html

And the patch makes clearer when the OpenMP allocators are actually used;
besides the obvious use via the routines above, it happens when using the
'allocate' directive/clause and the 'allocators' clause. The new note
is added to the beginning of the section

https://gcc.gnu.org/onlinedocs/libgomp/Memory-allocation.html

The new note mostly applies, except that only C supports 'omp allocate';
Fortran has a patch pending a comment by Jakub and for C++ I still need
to complete my daft patch.

I also fixed some typos (albeit 'behaviour' is not really a typo), removed
some 'kind=' for local consistency and to make especially the 'info' output
cleaner.

Comment, remarks, suggestions - before (or after) I apply it?

Tobias

PS: Also general comments and suggestions to the documentation are welcome.
The wording (current patch and current documentation) can surely be improved.

That documentation is missing - e.g. for several routines - is a known
problem.

If someone feels bored, besides reviewing libgomp.texi (6282 LoC),
https://gcc.gnu.org/projects/gomp/ (1281 LoC) and https://gcc.gnu.org/wiki/Offloading
(+ openmp + OpenACC) can surely be improved :-)
-----------------
Siemens Electronic Design Automation GmbH; Anschrift: Arnulfstraße 201, 80634 München; Gesellschaft mit beschränkter Haftung; Geschäftsführer: Thomas Heurung, Frank Thürauf; Sitz der Gesellschaft: München; Registergericht München, HRB 106955