Read fractal specification from a spec file.

Parameters

[in,out]	file	Spec file.
[in,out]	fractal	Fractal parameters.

The fractal parameters are all held constant for the simulation, and they are the same for all the particles.

The fractal data file is specified by the parameters:

frac_dim $d_{\rm f}$ (real, dimensionless): the fractal dimension (3 for spherical and less than 3 for agglomerate)
prime_radius (real, unit m): radius of primary particles
vol_fill_factor (real, dimensionless): the volume filling factor which accounts for the fact that even in a most closely packed structure the spherical monomers can occupy only 74% of the available volume (1 for compact structure)