This adds a new `splines` module which implements a high-level interface
for creating and evaluating splines and rewrite almost all modules to
use it. Also, notably:
1. both `simplespline` and DIERCKX splines can now used with a uniform
interface
2. most complexity due to handling working space arrays is gone
3. memory management has been significantly simplified too
This adds a new configuration file based on the INI format.
The new format will allow adding GRAY parameters without breaking
compatibility with existing configurations, unlike as of the old
gray_params.data.
This change structures the arguments of most functions, in particular
gray_main, into well-defined categories using derived types.
All types are defined in the gray_params.f90 (location subject to
change) and are organised as follows:
gray_parameters (statically allocated data)
├── antenna_parameters
├── ecrh_cd_parameters
├── equilibrium_parameters
├── misc_parameters
├── output_parameters
├── profiles_parameters
└── raytracing_parameters
gray_data - inputs of gray_main (dynamically-allocated arrays)
├── equilibrium_data
└── profiles_data
gray_results - outputs of gray_main (dynamically-allocated arrays)
