Some improvements to replay browser loading time.

- Parallelize metadata loading (this required some thread-safety adjustments in FieldLoader).
- Cache attribute lookups in FieldLoader as reflection is expensive.
- Don't use line.Contains('#') in MiniYaml.FromLines as this is actually a LINQ extension method and thus much slower than a call to string.IndexOf(char) or string.Contains(string).
Cleaned up the style of files related to the last commit.