Refactor the lexer/parser to expose friendlier words for scanning tokens. The preferr...

Refactor the lexer/parser to expose friendlier words for scanning tokens. The preferred top-level words now throw an exception on EOF.
CREATE -> scan-new
CREATE-CLASS -> scan-new-class
CREATE-WORD -> scan-new-word
CREATE-GENERIC -> scan-new-generic
scan -> (scan-token)
scan-token now throws on eof
(scan-word) returns word/number/f
scan-word now throws on eof
scan-word-name expects a non-number
Fixes #183.
Fixes #209.