Removed trailing whitespace from all .sml and .sig files.

This affects over 900 files and was done using emacs's delete-trailing-whitespace
function in batch mode. Building the system with Poly/ML and Moscow ML seems to
work, so I'm hoping these changes don't break anything. Please complain if
they do!

Updates on the software compiler:
1. Extend the front-end to handle polymorphism and higher order functions
2. Add primitive approaches to deal with pattern matching
3. Implement function calls in a caller save style
4. Fix a few bugs in existing source code