Implement axis targets, axis -> button and axis -> relative axis mappings. (#1)

Co-authored-by: Anna Rose Wiggins <annabunches@gmail.com>
Co-committed-by: Anna Rose Wiggins <annabunches@gmail.com>

internal/mappingrules/math.go

@@ -0,0 +1,30 @@
+package mappingrules
+
+import (
+	"golang.org/x/exp/constraints"
+)
+
+type Numeric interface {
+	constraints.Integer | constraints.Float
+}
+
+func Abs[T Numeric](value T) T {
+	return max(value, -value)
+}
+
+// LerpInt linearly interpolates between two integer values using
+// a float64 index value
+func LerpInt[T constraints.Integer](min, max T, t float64) T {
+	t = Clamp(t, 0.0, 1.0)
+	return T((1-t)*float64(min) + t*float64(max))
+}
+
+func Clamp[T Numeric](value, min, max T) T {
+	if value < min {
+		value = min
+	}
+	if value > max {
+		value = max
+	}
+	return value
+}