[Feature Request] Address to source file mappings

I'd like to have some way to figure out in what source file, and on what line a certain ROM address is located.

The reason behind this is because I do a lot of disassembly, and lately have been porting different version of crystal to pokecrystal, and have noticed I do this a lot.
I have a tool that helps me find the nearest label by reading the symfile, and figures out the filename through a dirty `grep`, and that helps me, but isn't always accurate and oftentimes requires hand-decoding the instructions by comparing with the hex editor. This is time-consuming.
I've also written tools around the formerly mentioned method, but they of course aren't as accurate as would be preferred.

I know this is a rather specific and maybe a bit out-of-the-way request for an assembler to implement properly, so I'd also be appreciative to get pointers as to how this could be achieved by hacking the codebase.