Red Squigglies

It would be nice if the errors/warnings returned by the compiler could be mapped directly onto the source code.

For this to work, the backend will need to move to a compile-rich endpoint, that serves up the error messages in a different way: they won't need the line info, and do need to be more structured so the squigglies can be placed in the correct parts of the div (see #10, which has similar problems). The reference compiler itself will need to be altered to support this, as it will need to dump json-encoded errors into a file, or otherwise pass back to the server, so that these can be fed backwards to the frontend.

These errors will go in their own tab as well though the ref-compiler should continue to output them as normal.