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/bs-logger/dist/logger/target.d.ts

@@ -0,0 +1,11 @@
+/// <reference types="node" />
+import { Writable } from 'stream';
+import { LogMessageFormatter } from './message';
+interface LogTarget {
+    stream: Writable;
+    minLevel: number;
+    format: LogMessageFormatter;
+}
+declare const parseLogTargets: (targetString?: string | undefined) => LogTarget[];
+declare const DEFAULT_LOG_TARGET: string;
+export { LogTarget, DEFAULT_LOG_TARGET, parseLogTargets };