This function is used to create a ParticleSet object from a vector/list of tab separated text files, each of one containing one line for each
particle in the related frame, alongside with its coordinates and if available, the computed features
The number of frames is also specified, as just a subset of the particle lists can be used for this
read.particles(particle.files, nframes = NULL)An object of the ParticleSet class
## see vignette and export.particles