`filter` parameter `fs.copy` and `fs.copySync`

Both `fs.copy` and `fs.copySync` have a new parameter filter which behaves like a whitelist.

`filter` can be a function or a regular expression

* for `filter:function`, `filter(srcPath)` must be true for copy
* for `filter:RegExp`, `filter.test(srcPath)` must be true for copy

`filter` is optional for both `fs.copy()` and `fs.copySync()`