small tweaks

   .. tab:: CMake build

      With CMake the choice of integer types is made via setting a

      variable during configuration.

      .. code-block:: bash

         -D LAMMPS_SIZES=value   # smallbig (default) or bigbig or smallsmall

      If the variable is not set explicitly, "smallbig" is used.

   .. tab:: Traditional build

      If you want a setting different from the default, you need to edit your

      machine Makefile.

      If you want a setting different from the default, you need to edit the

      ``LMP_INC`` variable setting your machine Makefile.

      .. code-block:: make

* image flags = roll over at about 1 million (2\^20)

The "smallsmall" setting is only needed if your machine does not

support 8-byte integers.  It allows for:

support 64-bit integers.  It allows for:

* total atom count = 2\^31 atoms (about 2 billion)

* total timesteps = 2\^31 (about 2 billion)

Regardless of the total system size limits, the maximum number of atoms

per MPI rank (local + ghost atoms) is limited to 2 billion for atomic

systems and 500 million for systems with bonds (due to using the 2

upper bits of the local atom index for storing special bonds labels).

systems and 500 million for systems with bonds (the additional

restriction is due to using the 2 upper bits of the local atom index

in neighbor lists for storing special bonds info).

Image flags store 3 values per atom in a single integer which count the

number of times an atom has moved through the periodic box in each

def replace_tabs_handler(app, docname, source):

    """ When builder is not 'html', remove 'tabs' directive

    and replace 'tab' directive with 'admonition'"""

    and replace any 'tab' directive with 'admonition'"""

    if app.builder.name != 'html':

        for i in range(len(source)):

            str = source[i].replace('.. tabs::','')