- Changed all the goto &Math::* calls to regular function calls.

This may prevent some memory leaks in some special cases.

One such example, is the following, which used over 500 MB of RAM:

    use Sidef;

    my $n = Sidef::Types::Number::Number->new(0);
    my $d = Sidef::Types::Number::Number->new(6);

    my $digits = $d x $d;
    foreach my $k (1..1e6) {
        push @list, $n if index($n->inc->pow($d)->mul($d), $digits) >= 0
    }

Now, the above code requires only 25 MB of RAM.

lib/Sidef/Types/Number/Number.pm

@@ -664,7 +664,7 @@ package Sidef::Types::Number::Number {
       Math_GMPz: {
 
             if (Math::GMPz::Rmpz_fits_ulong_p($x)) {
-                goto &Math::GMPz::Rmpz_get_ui;
+                return Math::GMPz::Rmpz_get_ui($x);
             }
 
             state $t = Math::GMPz::Rmpz_init_set_str_nobless(join('', ~0), 10);
@@ -690,8 +690,7 @@ package Sidef::Types::Number::Number {
       Math_MPFR: {
 
             if (Math::MPFR::Rmpfr_integer_p($x) and Math::MPFR::Rmpfr_fits_ulong_p($x, $ROUND)) {
-                push @_, $ROUND;
-                goto &Math::MPFR::Rmpfr_get_ui;
+                return Math::MPFR::Rmpfr_get_ui($x, $ROUND);
             }
 
             if (Math::MPFR::Rmpfr_number_p($x)) {
@@ -718,11 +717,11 @@ package Sidef::Types::Number::Number {
       Math_GMPz: {
 
             if (Math::GMPz::Rmpz_fits_slong_p($x)) {
-                goto &Math::GMPz::Rmpz_get_si;
+                return Math::GMPz::Rmpz_get_si($x);
             }
 
             if (Math::GMPz::Rmpz_fits_ulong_p($x)) {
-                goto &Math::GMPz::Rmpz_get_ui;
+                return Math::GMPz::Rmpz_get_ui($x);
             }
 
             return;
@@ -743,13 +742,11 @@ package Sidef::Types::Number::Number {
 
             if (Math::MPFR::Rmpfr_integer_p($x)) {
                 if (Math::MPFR::Rmpfr_fits_slong_p($x, $ROUND)) {
-                    push @_, $ROUND;
-                    goto &Math::MPFR::Rmpfr_get_si;
+                    return Math::MPFR::Rmpfr_get_si($x, $ROUND);
                 }
 
                 if (Math::MPFR::Rmpfr_fits_ulong_p($x, $ROUND)) {
-                    push @_, $ROUND;
-                    goto &Math::MPFR::Rmpfr_get_ui;
+                    return Math::MPFR::Rmpfr_get_ui($x, $ROUND);
                 }
             }
 
@@ -1063,46 +1060,44 @@ package Sidef::Types::Number::Number {
       Math_GMPz: {
 
             if (Math::GMPz::Rmpz_fits_slong_p($x)) {
-                goto &Math::GMPz::Rmpz_get_si;
+                return Math::GMPz::Rmpz_get_si($x);
             }
 
             if (Math::GMPz::Rmpz_fits_ulong_p($x)) {
-                goto &Math::GMPz::Rmpz_get_ui;
+                return Math::GMPz::Rmpz_get_ui($x);
             }
 
-            goto &Math::GMPz::Rmpz_get_d;
+            return Math::GMPz::Rmpz_get_d($x);
         }
 
       Math_GMPq: {
 
             if (Math::GMPq::Rmpq_integer_p($x)) {
-                @_ = ($x = _mpq2mpz($x));
+                $x = _mpq2mpz($x);
                 goto Math_GMPz;
             }
 
-            goto &Math::GMPq::Rmpq_get_d;
+            return Math::GMPq::Rmpq_get_d($x);
         }
 
       Math_MPFR: {
-            push @_, $ROUND;
-
             if (Math::MPFR::Rmpfr_integer_p($x)) {
                 if (Math::MPFR::Rmpfr_fits_slong_p($x, $ROUND)) {
-                    goto &Math::MPFR::Rmpfr_get_si;
+                    return Math::MPFR::Rmpfr_get_si($x, $ROUND);
                 }
 
                 if (Math::MPFR::Rmpfr_fits_ulong_p($x, $ROUND)) {
-                    goto &Math::MPFR::Rmpfr_get_ui;
+                    return Math::MPFR::Rmpfr_get_ui($x, $ROUND);
                 }
             }
 
-            goto &Math::MPFR::Rmpfr_get_d;
+            return Math::MPFR::Rmpfr_get_d($x, $ROUND);
         }
 
       Math_MPC: {
             my $r = Math::MPFR::Rmpfr_init2(CORE::int($PREC));
             Math::MPC::RMPC_RE($r, $x);
-            @_ = ($x = $r);
+            $x = $r;
             goto Math_MPFR;
         }
     }
@@ -1117,8 +1112,7 @@ package Sidef::Types::Number::Number {
         goto(ref($x) =~ tr/:/_/rs);
 
       Math_GMPz: {
-            push @_, 10;
-            goto &Math::GMPz::Rmpz_get_str;
+            return Math::GMPz::Rmpz_get_str($x, 10);
         }
 
       Math_GMPq: {
@@ -5345,15 +5339,15 @@ package Sidef::Types::Number::Number {
         goto(ref($x) =~ tr/:/_/rs);
 
       Math_MPFR: {
-            goto &Math::MPFR::Rmpfr_sgn;
+            return Math::MPFR::Rmpfr_sgn($x);
         }
 
       Math_GMPq: {
-            goto &Math::GMPq::Rmpq_sgn;
+            return Math::GMPq::Rmpq_sgn($x);
         }
 
       Math_GMPz: {
-            goto &Math::GMPz::Rmpz_sgn;
+            return Math::GMPz::Rmpz_sgn($x);
         }
 
       Math_MPC: {