Represents the work of 5 commits

Fixes the atomic class slot names

o now all slot names of the atomic classes for the citation types
  are named after the class.

Puts "citation" slot in place for "eml"

This is related to issue #27

Adds more coercion methods for literature classes

o This belongs to issue #27

Changes documentation and inclusion

o Adds the modules to be included into the literature module
	- adds modules already there for inclusion
o changes the citation prototype in comments

defines XML/S4 coercions for citation class, corrects them for article class #27
Merge pull request #73 from cpfaff/litrature

Fixes XML coercion definitions for literature module
- makes class slot names match definitions (for all complex types)
- fixes coercion definitions, using S4Toeml where appropriate
- defines missing coercion definitions
- Also adds citation class as a slot for the eml module (eml.R)