Fixed FStack / CompilerFlag bug . Made DOC for Word.

1. Fixed CompileFlag / Block Bug: when still backup flag but didn't
involve block tokens.
2. Fixed Signature bug when not valid data.
3. Made DOC for Words. Access by "DOC" word.
4. Can now make instance inside word definition ( due to fixed bug at
(1) )
5. Word can also be used as variables. So we don't need another variable
stack. One for both.