Add .dropboxignore directory to exclude folders without using selective sync

This is a necessity for power users. As mentioned by others, some of use have folders with 10000 small files that are updates very frequently but that we don't want to sync. For instance node_modules when working on Node.js projects. Another example is that some of my projects have an sqlite database in the folder that I don't want to sync every 5 seconds because a byte changed somewhere.

It doesn't need to be a complex thing, just for users that know what they are doing.I don't even need a fancy way of defining rules, an easy solution is if  a".dropboxignore" file is detected in a folder the folder and it's children could be ignored by dropbox.