Changed sign for the accelerated boundary frame
Implemented pressure-gradient-based boundary force, using midpoint scheme. It's zero near any boundary.
Repaired incorrect check for fitting the lattice size to the box size.
Made some minor style and x -> x.0f modifications
Made modifications to the accelerated frame transform. Figured out that it does NOT work this way and should be repaired.
Worked on accelerated frame and added some guards around the related functions, as well as around those related to the reaction. Still need to check units, correct the mass of the fluid, check if it works without ext_force, etc. etc.