feat: base path is relative to file's current path

The file base path is good in most cases. However when using a glob pattern to grab files it is helpful for the base option to be relative to the file streams current base path.

For example
When using a glob pattern ```foo/**/*.html```
With a file
foo/bar/biz/baz.html

You get a file stream of:
base: foo/
path: foo//bar/biz/baz.html