Resolve full file paths when copying files
Resolve full file paths when copying files

Currently, the `copy_files` function doesn't support symlink files due to
its use of `DirEntry::metadata` - To avoid this issue, this patch
resolves the file path first before checking for metadata.

Fixes #1157

azerupi/mdBook,azerupi/mdBook,azerupi/mdBook,azerupi/mdBook