Corrected parsing of sign numbers in the interpreter.
Made UM/MOD a native word and implemented it in the interpreter.
EMIT in the interpreter no longer crash on negative numbers.
Added S>D and ABS.
Added SPACE and SPACES.
Ensure BASE gets a default value by calling DECIMAL.
Added free field numeric output words.

This adds . and U. words.

Also added building block words <# #> # HOLD SIGN and #S
Removed the unused core.fth file.