A better alternative for source code file browsing than finder+quicklook? I'm not an IDE user and I spend a lot of time going back and forth between finder windows opening files in quicklook just to look at a thing here and there. This gets awkward fast, specially as QL loses the spot I was reading at, and the file browser is not as attuned to this usage as that of an IDE file browser. Also, the QLStephen source code preview stops working from time to time. 

I'm wondering, is there any lightweight alternative to browsing source files like this?A finder replacement, a terminal utility, or something like those old school image file browsers ala ACDSee but for text?

I'd be happy if the column view of the finder showed me a full pane scrollable preview of the text so I didn't have to open QL, but other desirable features would be the ability to set a project folder with a file tree in the sidebar, bookmarking folders/files, search across project folder, and dreaming big, the possibility to go to function definition. 
Been thinking to write something like it myself but I just keep thinking something like it must exist somewhere.
BBEdit is able to have multiple documents open at one time and then there is a left side sidebar you can easily change between documents. In the menu bar go to VIEW > Show Sidebar. It appears to keep your highlights and scrolling of each document. You can use BBEdit for free without paying for it as well but it will ask for you to pay for the first couple weeks. BBEdit has markers, grep find/replace, and multi-file search as well. Sounds like a lot of what you want.