[MLton] MLton library project

[Matthew Fluet]

> Also, compile time with MLton seems to increase (significantly) with
> that approach.  I don't know the exact reasons for this, but I'd guess that the
> necessary namespace / environment management (although probably quick) isn't
> free.

This could probably be improved, although Stephen will know better.  The 
mechanism for saving and restoring bases for MLBs is based on taking 
snapshots of the environment, which I don't believe is all that efficient. 
It is the same mechanism that saves and restores the environment for 
functors.