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/function-bind/test/.eslintrc

@@ -0,0 +1,9 @@
+{
+	"rules": {
+		"array-bracket-newline": 0,
+		"array-element-newline": 0,
+		"max-statements-per-line": [2, { "max": 2 }],
+		"no-invalid-this": 0,
+		"no-magic-numbers": 0,
+	}
+}