Prevent doxygen from creating large graphs

With the upgrade to doxygen 1.8.8, for some reason dot is having trouble
creating some of the larger graphs, causing dot to seg-fault. This
change disable the include and included by graphs, that are very large.
Also, limit the number of levels the graphs will go, from unlimited to
2. This also has the advantage of making sure the graphs don't get too
large.
Fix doxygen issue with static_assert

It appears that doxygen 1.8.8 has a problem with static_assert. ie, it
can't find declarations for functions defined after static_assert. To
sidestep this issue, this changes the template parameter (BlockSize)
from int to size_t. So there is no longer a need to call static_assert
to make sure BlockSize is greater than zero.