4.0-6:
 * Improving parse.formula function
 * Renamed 'parse.formula' to 'parseFormula', to avoid name confusion and
   adhere to common naming standards in Zelig.

4.0-5 (August 25th, 2011):
 * Removed dependency on 'iterators' package
 * Updated NAMESPACE and DESCRIPTION files correspondingly
 * Restructured internals of 'zelig' function
 * Added CHANGES file to summarize detail-oriented code changes
 * Print methods for multiply-imputed data-sets have been improved
 * Print methods for setx objects have been improved
 * zelig now returns a specially constructed list when handling multiply-
   imputed data-sets
 * The 'state' variable has been added to the the zelig and MI objects.
   This variable stores shared information between an "MI" (zelig-list) object
   and all its children.
 * Beautified output of print.setx
 * Added terms.zelig as a method with documentation
 * Added a 'formula' index to the 'zelig' class. This contains a formula
   formula identical that contained in the result index (within the zelig 
   object)
 * Added "old-formula" variable to the "state" attribute (this attribute is an
   environment. That is, the attribute "state", which is an environment, now
   contains a variable titled "old-formula". This specifies the original
   formula submitted to the 'zelig' function
