sorry, bugfix: with-gensyms
several eval-whens were necessary
documentation: defpackage, pkg-local-nickname, syntax (#34)
Merge branch 'master' of git://github.com/guicho271828/cl21 into guicho271828-master
keep-if & nkeep-if must refer cl21:remove-if-not and cl21:delete-if-not, not CL one.