fix: hardcoded '/' in normalized options.fs, fixes #412, #408

Changes including:
- will not call fs.resolve when normalizing `fs`
- removed hardcoded `/`
- mandatory `fs.dirname` for relative reference
- mandatory `fs.sep`, defaults to '/'

package.json

@@ -14,6 +14,7 @@
     "lint": "eslint \"**/*.ts\" .",
     "check": "npm test && npm run lint",
     "test": "nyc mocha \"test/**/*.ts\"",
+    "test:e2e": "mocha \"test/e2e/**/*.ts\"",
     "perf": "cd benchmark && npm ci && npm start",
     "perf:diff": "bin/perf-diff.sh",
     "perf:engines": "cd benchmark && npm run engines",