Added Subs class

Author: rajithv

ext/symengine/symengine.c

@@ -93,6 +93,9 @@ void Init_symengine() {
     rb_define_const(m_symengine, "E", cconstant_e());
     rb_define_const(m_symengine, "EULER_GAMMA", cconstant_euler_gamma());
     rb_define_const(m_symengine, "I", cconstant_i());
+    
+    //Subs class
+    c_subs = rb_define_class_under(m_symengine, "Subs", c_basic);
 
     //Add class
     c_add = rb_define_class_under(m_symengine, "Add", c_basic);

ext/symengine/symengine.h

@@ -15,6 +15,7 @@ VALUE c_rational;
 VALUE c_complex;
 VALUE c_complex_double;
 VALUE c_constant;
+VALUE c_subs;
 VALUE c_add;
 VALUE c_mul;
 VALUE c_pow;

ext/symengine/symengine_utils.c

@@ -95,6 +95,8 @@ VALUE Klass_of_Basic(const basic_struct *basic_ptr) {
             return c_complex_double;
         case SYMENGINE_CONSTANT:
             return c_constant;
+        case SYMENGINE_SUBS:
+            return c_subs;
         case SYMENGINE_ADD:
             return c_add;
         case SYMENGINE_MUL: