xenc-schema.rnc

Dear colleagues,

Attached please find the first version of xenc-schema.rnc.  

I have not created the schema for encryption 1.1.  Moreover, I 
have not created driver files or other helper modules.  However, the
attached schema is the most important one.  

You comments are very welcome.   In particular, could you 
please review my understanding of the interaction between 
the value of @Algorithm and permissible 
children (parameters)?

Regards,

SC34/WG4 Convenor
MURATA Makoto (FAMILY Given)