[Yhc] Yhc .hi format docs

[Neil Mitchell]

Hi Robert,

> Is there any documentation/dev notes/anything helpful having to do
> with the Yhc interface file format?
They are identical to the nhc98 ones, so if you can find any docs for
the nhc98 stuff its reuseable

> I couldn't find anything on the wiki and trying to read the code for
> the parser and printer made my head hurt.  They're both written in a
> style that's a little, uh... less than transparent.
The code is also directly from nhc98, with no modifications.

Me and Tom have discussed this - moving to binary .hi files makes a
lot of sense and will give quite large compile time speedups. Also,
shoving the .hi information in the .hbc file is not a bad idea, since
we already have a binary file sitting around and its useful type
information that could be used to do a static type check on the .hbc
file, similar to Java's verifier.

The only thing to remember is that .hi files are written manually for
a couple of things to bootstrap stuff.

Thanks

Neil