added generic ecore:external method that returns object's external
  representation (S-expression)
defined ecore:external for template
defined eenv:template-names
defined exil:environments - returns list of symbols
defined exil:current-environment - returns symbol
defined exil:deftemplatef as functional counterpart for teftemplate
defined exil:find-template - returns template's external representation
defined exil:templates - returns list of symbols
updated packages and functional integration test