eolian: drop Eina_Value

eolian: drop Eina_Value

Because of Eina_Value being less than optimal in our usage, we're dropping it in Eolian.
This simplifies the code and makes it easier to bind to other languages, which
will aid new generators. Also, we're dropping long double support from eo files
and expressions as it causes an ABI breakage in gcc 4.4.