registerWithAttributes

Add attributes parameter for additional registration info (for example: email). 

XEP-0077: In-Band Registration
Ref: http://xmpp.org/extensions/xep-0077.html

\<iq type='set' id='reg2'\>
  \<query xmlns='jabber:iq:register'\>
    \<username\>bill\</username\>
    \<password\>Calliope\</password\>
    \<email\>bard@shakespeare.lit\</email\>
  \</query\>
\</iq\>