Added support for some publishers in src/api/classes.lisp

* src/api/conversion.lisp (header): updated copyright
  (keyword/downcase): new type; like `cl:keyword' but the symbol name
  should be downcased when converting to XML
  (xml-> string eql keyword/downcase): new method; deserialize
  objects of type `keyword/downcase'
  (->xml symbol eql string eql keyword/downcase): new method;
  serialize objects of type `keyword/downcase'
* src/api/classes.lisp (define-interface-implementations publisher):
  new interface; rough descriptions of some common publisher
  implementations
  (define-model-class job): added `publisher' slot, values of
  implementations of the `publisher' interface
Extended README.org

* README.org: extended meta-data; extended section on modifying jobs;
  adding TODOs for missing sections