Add .dropboxignore directory to exclude folders without using selective sync

Please please please can you add a feature that allows folders to be excluded from the Dropbox account (on windows and mac). For sure I'm not the first person to request this, but I'm yet to find a good explanation of why it's not there. A quick google search reveals loads of people also looking for the same feature. I really like the workflow I have with dropbox, but it's getting to the point where I might switch providers in order to allow better selective sync.

I've seen hackish solutions using selective sync, but it would be great if this could be done in one of the following ways:
- global pattern matching eg "node_modules"
- a marker file in the directory like .dropboxignore
- a simple right click context menu "Ignore this folder"

Other than that, keep up the good work. Cheers.
Tom