This scheme of "when we handle line-by-line, compile one word at a time then
execute" so that we could allow words like "CREATE" to call "readword" before
continuing was a bad scheme. It made things like branching outside of a colon
definition impossible.
This commit implement a new "litWord". When an undefined word is encountered at
compile time, it is included as-is in a string literal word. It is at run time
that we decide what to do with it.
