Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/kleur/kleur.d.ts

@@ -0,0 +1,45 @@
+// Originally by: Rogier Schouten <https://github.com/rogierschouten>
+// Adapted by: Madhav Varshney <https://github.com/madhavarshney>
+declare namespace kleur {
+	interface Color {
+		(x: string | number): string;
+		(): Kleur;
+	}
+
+	interface Kleur {
+		// Colors
+		black: Color;
+		red: Color;
+		green: Color;
+		yellow: Color;
+		blue: Color;
+		magenta: Color;
+		cyan: Color;
+		white: Color;
+		gray: Color;
+		grey: Color;
+
+		// Backgrounds
+		bgBlack: Color;
+		bgRed: Color;
+		bgGreen: Color;
+		bgYellow: Color;
+		bgBlue: Color;
+		bgMagenta: Color;
+		bgCyan: Color;
+		bgWhite: Color;
+
+		// Modifiers
+		reset: Color;
+		bold: Color;
+		dim: Color;
+		italic: Color;
+		underline: Color;
+		inverse: Color;
+		hidden: Color;
+		strikethrough: Color;
+	}
+}
+
+declare let kleur: kleur.Kleur & { enabled: boolean };
+export = kleur;