I have many todo files in markdown format scattered on my directories tree. I like to keep it this way because my todo files stay in each project folder. But I also like to get a global overview of what to do in all my projects, so I'm using for now a small script that read a list of paths to those files, concatenate the files into a single file. I'm using geany for opening this file. If I want to modify anything, I need to open the original file, save it and reapply my script.

I'm wondering if anyone knows a software/geany plugin/atom plugin that would be able to open those multiple files in the same view. 
Ideally, I would like to be able to:

* fold/expand files one by one
* save any modification in the view directly on the original .md file
* syntax coloration, though I could do without
* open source

Yet, I haven't found something closer to that than my concatenation. Any idea ?

Thanks a lot!