Created a `SplineStruct` struct

[rvishnkr]

Contains variables that were previously global

struct SplineStruct{
    //----------------------------------------//
    //------Parameters for Interpolation------//
    //----------------------------------------//
    int r_cnt;          // Number of vertical points
    int accel;          // Acceleration index
    double* r_vals;     // r_k elements (r_cnt length)
    static double* T_vals;    // Temperature at r_k
    static double* u_vals;    // E-W winds at r_k
    static double* v_vals;    // N-S winds at r_k
    static double* rho_vals;  // Density at r_k
    //----------------------------------------------------//
    ////-------------Combined Function to Input-------------//
    ////------G2S Files and Generate the Interpolation------//
    ////----------------------------------------------------//
    static struct NaturalCubicSpline_1D Temp_Spline;
    static struct NaturalCubicSpline_1D Windu_Spline;
    static struct NaturalCubicSpline_1D Windv_Spline;
    static struct NaturalCubicSpline_1D Density_Spline;
};

Declaration: Code/Atmo/G2S_GlobalSpline1D.h
Initialization: Code/GeoAcGlobal_main.cpp

This struct needs to be passed to the c() function but there seem to be almost 100+ calls to it, so we need to isolate the ones we need and change it.