[Nickle]UTF8 and bool type

[Keith Packard]

I'd like to propose a couple of changes to nickle, the first is to switch
the string representation to Unicode.  Strings will appear as a sequence of
32-bit Unicode values.  Strings read and written in "raw" form will be
encoded using UTF-8.  The internal representation is also UTF-8, but this 
isn't visible to applications.

Three new File namespace functions are needed:

 File::getcharacter (file f)		- parse the next UTF-8 char
 File::ungetcharacter (int c, file f)	- push the specified char back as UTF-8
 File::putcharacter (file f)		- output c in UTF-8 format

As always, suggestions for the names are welcome.

The second change is a bit more fundemental.  Nickle has always allowed any
type to appear in expressions where a boolean value was needed; the test 
was always whether the computed value was not equal to 0.  I propose to 
add a real boolean type (name bool).  This type will have two values, 
'true' and 'false' and will be the required type for all primitive 
conditional tests (if, while, do, for, twixt, ?:).

The 'bool' type will be extremely useful in the future as algebraic types 
are added, but even now, it should catch a large class of errors which 
would otherwise go undetected.

-keith