Adding ability to have a manifests cache

By using a manifests cache, we can prevent the startup time from having to perform another Glob every time. This saves 5-6 seconds on EVERY startup. To clear the cache, simply remove the cache file.

@intervalia / @redbugz, any thoughts?
in that case this would just replace the dot, leaving the leading slash, and you would end up with double slashes. But as long as the library ignores the double slash, I supposed it will work.
And if I did a relative path ../path/to file, it would leave it ./path/to/file, right?