Add .dropboxignore directory to exclude folders without using selective sync

There needs to be a way to specify ignore folders/files that are software generated, intended to be temporary and local to a specific machine. For instance Microsoft Visual Studio generates a /bin and /obj upon building code, which a developer could do a hundred a times a day. Each time the software deletes the folder and recreates it. Which now you have to close dropbox because it dropbox locks up the folder and Visual Studio fails to build then.  You current process of ignoring a folder is also flawed in another way because it doesn't persist when the temporary folder might be automatically deleted by a program. Maybe borrowing a page from the .git code repository world, a simple solution would be too look for a file named .dropbox_ignore.txt with specified relative paths to ignore like /bin /node_modules /obj.