Adding upstream version 2.1.2.

Signed-off-by: Daniel Baumann <daniel@debian.org>

range.go

@@ -0,0 +1,43 @@
+package chart
+
+// NameProvider is a type that returns a name.
+type NameProvider interface {
+	GetName() string
+}
+
+// StyleProvider is a type that returns a style.
+type StyleProvider interface {
+	GetStyle() Style
+}
+
+// IsZeroable is a type that returns if it's been set or not.
+type IsZeroable interface {
+	IsZero() bool
+}
+
+// Stringable is a type that has a string representation.
+type Stringable interface {
+	String() string
+}
+
+// Range is a common interface for a range of values.
+type Range interface {
+	Stringable
+	IsZeroable
+
+	GetMin() float64
+	SetMin(min float64)
+
+	GetMax() float64
+	SetMax(max float64)
+
+	GetDelta() float64
+
+	GetDomain() int
+	SetDomain(domain int)
+
+	IsDescending() bool
+
+	// Translate the range to the domain.
+	Translate(value float64) int
+}