option to write Par_file for specfem

[aakash10gupta]

In lines with #18, the option to generate a Par_file will be helpful. In general use of the specfem package, a user typically starts with a Par_file template from a specfem example and modifies it for their use case. tomo_helper providing this template seems natural and can be the default option.

Also, the parameters UTM_PROJECTION_ZONE, SUPPRESS_UTM_PROJECTION, NPROC, DT, MODEL, ANISOTROPY, can be updated automatically based on the parameters and mesh designing (#21 ) by tomo_helper.