feat: Add Float.round (#1301)

Just a wrapper around the c std function.

core/Float.carp

@@ -14,6 +14,7 @@ suffixed with `f`.")
   (register to-bytes (Fn [Float] Int))
   (register from-int (Fn [Int] Float))
   (register copy (Fn [(Ref Float)] Float))
+  (register round (Fn [Float] Int))
 
   (register = (Fn [Float Float] Bool))
   (register < (Fn [Float Float] Bool))

core/carp_float.h

@@ -130,3 +130,7 @@ float Float_floor(float x) {
 float Float_mod(float x, float y) {
     return fmodf(x, y);
 }
+
+int Float_round(float x) {
+  return roundf(x);
+}