[plt-scheme] A new version of Typed Scheme

In the current SVN version, and in the next release, Typed Scheme now
has a new name.  Typed modules should now use the language
`typed/scheme', or `typed/scheme/base', like this:

#lang typed/scheme
(: x Number)
(define x 7)

The `typed/scheme' language is like `scheme', but checked, and
`typed/scheme/base' is like `scheme/base'.  I hope to add `typed/'
versions of additional languages in the future.

This change also brings with it a refactoring of the numeric hierarchy
in Typed Scheme.  Numbers are now given more precise types, and
several functions (such as `vector-ref') require more precise types.
The existing `typed-scheme' language will continue to work as it did
previously.

Finally, the new release comes with a rewritten version of the guide
to Typed Scheme, available soon at
http://pre.plt-scheme.org/docs/html/ts-guide/.  I'm very interested in
feedback on the new guide.
-- 
sam th
samth at ccs.neu.edu