Be able to parse F77
Several people expressed interest in parsing F77. This will probably have to be a separate parser from our modern Fortran parser, but the we might be able to reuse most of our AST, and almost for sure the ASR should be able to represent F77 natively, as I think the semantics of F77 and F2018 hasn't changed for the most part.
We should also extend our ASR -> AST -> source code generator to optionally support F77.
There is a lot of F77 code still in use, and given that I don't think it will complicate LFortran's design (on the contrary I think it fits exactly into our goals), this would be a very useful capability for a lot of people.
(I thought we already have an issue for this, but I couldn't find it.)