REORG: include: move integer manipulation functions from standard.h to intops.h

REORG: include: move integer manipulation functions from standard.h to intops.h

There are quite a number of integer manipulation functions defined in
standard.h, which is one of the reasons why standard.h is included from
many places and participates to the dependencies loop.

Let's just have a new file, intops.h to place all these operations.
These are a few bitops, 32/64 bit mul/div/rotate, integer parsing and
encoding (including varints), the full avalanche hash function, and
the my_htonll/my_ntohll functions.

For now no new C file was created for these yet.