math: add a pure V math.mathutil, with generic min, max and abs functions (#9176), and use it consistently

vlib/math/mathutil/mathutil.v

@@ -0,0 +1,31 @@
+// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+module mathutil
+
+[inline]
+pub fn min<T>(a T, b T) T {
+	if a < b {
+		return a
+	} else {
+		return b
+	}
+}
+
+[inline]
+pub fn max<T>(a T, b T) T {
+	if a > b {
+		return a
+	} else {
+		return b
+	}
+}
+
+[inline]
+pub fn abs<T>(a T) T {
+	if a > 0 {
+		return a
+	} else {
+		return -a
+	}
+}