Added support for string literals.

Added STRING, to compile a string embedded in 'lit'.
Made 'lit' create an addressable string on the fly.
Added XT-LIT, to allow for compiling execution tokens as string literals.

Intended to be a building block for 'tick' and POSTPONE.
Fixed PARSE and added SRC-SPAN

PARSE now updated >IN to point past the delimiter if present.
SRC-SPAN prepares for looping over current input stream and is
used by PARSE, ( and SKIP.
Added 'tick'
Fixed POSTPONE and ABORT"

Removed (ABORT") and let ABORT" handle it.