Delete abstract-reduce for hash-tables.
Make append allow to take abstract-sequences.
(refs #38) Delete map-into.
(refs #38) Change the specification maphash. It returns a hash-table now.
Add make-sequence-iterator for abstract-hash-table.
(refs #38) abstract-maphash isn't needed anymore. make-sequence-iterator makes it work.
Add a documentation about Abstract Classes.
Add a documentation about reader macros of CL21.
Fix README.
Delete CHANGES.markdown.
Merge branch 'master' of git://github.com/guicho271828/cl21 into guicho271828-master

Conflicts:
	README.markdown
Import with-gensyms for doeach.
Fix README. mapcar was deleted.
Delete length=.
Rename split-sequence(-if) -> split(-if).
CL-Utilities isn't used anymore.
Add push-back, pushnew-back and pop-back.
Make last-cons allow to take abstract-list.
Define emptyp & getf for abstract classes.
Merge branch 'master' of git://github.com/guicho271828/cl21 into guicho271828-master