first commit: added SDPD

cmake/CMakeLists.txt

cmake/presets/all_off.cmake

cmake/presets/all_on.cmake

cmake/presets/manual_selection.cmake

cmake/presets/nolib.cmake

cmake/presets/std.cmake

cmake/presets/std_nolib.cmake

cmake/presets/user.cmake

doc/src/Commands_fix.txt

doc/src/Commands_pair.txt

doc/src/Packages_details.txt

doc/src/Packages_user.txt

doc/src/fix.txt

doc/src/fix_meso_move.txt

doc/src/fix_rigid_meso.txt

doc/src/fixes.txt

doc/src/lammps.book

doc/src/pair_sdpd_taitwater_isothermal.txt

doc/src/pair_style.txt

doc/src/pairs.txt