Support arbirary offsets in peek-character
Make read-character always take two args
Add an arg to consume-character indicating the number of chars to consume

And rename to istream-consume.
Support arbitrary read-ahead for input streams
Avoid doing make-buffer-ostream for each token read
Don't do make-string-istream when parsing an integer
Introduce #f, #t, #u syntax for special values

false, true and unspecified look too much like symbols, both for humans
and in terms of reader efficiency.