Writing and reading of general anisotropy parameters to and from binary format gll model files

[aakash10gupta]

This pull request adds the following two features -

1. Writing out of general anisotropy parameters as 21 binary format files when the model is anisotropic i.e. ANISOTROPY = .true.
2. Reading of general anisotropy parameters from 21 binary format gll model files when the model is anisotropic i.e. ANISOTROPY = .true. and the model type i.e. MODEL = gll

The typical binary format gll model files for one of the 21 general anisotropy parameters say c23 would be named proc******_c23.bin