Add new TASK_VERSION special variable

Closes #1014
Closes #990

internal/version/version.go

@@ -0,0 +1,25 @@
+package version
+
+import (
+	"fmt"
+	"runtime/debug"
+)
+
+var version = ""
+
+func GetVersion() string {
+	if version != "" {
+		return version
+	}
+
+	info, ok := debug.ReadBuildInfo()
+	if !ok || info.Main.Version == "" {
+		return "unknown"
+	}
+
+	ver := info.Main.Version
+	if info.Main.Sum != "" {
+		ver += fmt.Sprintf(" (%s)", info.Main.Sum)
+	}
+	return ver
+}