Simplified the code for dealing with the remainder particles

Simplified the kview computation to get the inclusion of particles with a kernel that intersects the field of view, despite the particle being outside of it

Correct kview computation to remove the inclusion of particles with hsml[i] < 0 (equivalent to the old zpart > 0 condition)

Detangle tt between the kernel pixel size (the tt variable) with the kernel projected size (the new tt_f float variable), allowing kernels with sizes under the resolution to be computed properly

Adding "-ffast-math" compiler flag by default. This speeds up the code by more than a factor of 3.

…py-sphviewer, upgrading to version 1.2.1