filter parameter fs.copy and fs.copySync

[sri-rang]

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

[sri-rang]

This changes the interface of fs_extra.copy()

from: fs_extra.copy(src, dest, callback)

to: fs_extra.copy(src, dest, filter, callback)

This probably could be avoidable :-/

[jprichardson]

Ya, filter should be optional... but that's not too hard of a modification.

[sri-rang]

Yeah, I'll close this pull request, make filter optional, squash commits and send you another PR. ;-)