More structured text editor for TODOs?

I have a TODO.txt file in every project I work on, which is just a list of things to do, a record of what happened when I did them, any difficulties, etc. etc. This might potentially include code things like snippets, links, database values.

So far a normal text file has worked fine but I'm wondering if there is something better, particularly with folding, so as the file gets larger I can fold sections away. Markdown is the obvious candidate but neither of the plugins in Pycharm (markdown navigator, markdown support) has folding, and I am not interested in a separate preview window, I want to see the structure in the text while I'm writing it.

I also looked at the restructured text plugin but it doesn't have folding. I thought about html or haml but it's a bit over the top. The best plugin I've found so far is org4idea, which does have folding and comments.

Any other ideas?