Full calendar item update support

[gshutler]

CalendarItem#update_item! did not support the full range of options available via the EwsBuilder#build_xml! method as :text was the only reserved attribute preserved and a nested structure was not supported at all.

This commit makes :sub_elements and :xmlns_attribute reserved too and ensures that any nested structures are also escaped as necessary.

[gshutler]

I think I have a %i{} in here, didn't realise tests ran against 1.9.3, will fix.

[GeorgeDewar]

Hi @gshutler, I've been trying to using update_item! to update attendees on a meeting. It looked like this PR might be adding the required support, but I still have not been able to get it to work with your code.

I'm calling it like:

new_attendee = [{:name=>{:text=>"General User"}},
                        {:email_address=>{:text=>"[email protected]"}},
                        {:routing_type=>{:text=>"SMTP"}},
                        {:mailbox_type=>{:text=>"Mailbox"}}]
@calendar_item.update_item!(
  updates: { required_attendees: new_attendee },
  send_meeting_invitations_or_cancellations: "SendToAllAndSaveCopy",
)

The Updates section of the request ends up looking like:

<t:Updates>
    <t:SetItemField>
      <t:FieldURI FieldURI="calendar:RequiredAttendees"/>
      <CalendarItem xmlns="http://schemas.microsoft.com/exchange/services/2006/types">
        <RequiredAttendees>[{"Name"=&gt;{:text=&gt;"General User"}}, {"EmailAddress"=&gt;{:text=&gt;"[email protected]"}}, {"RoutingType"=&gt;{:text=&gt;"SMTP"}}, {"MailboxType"=&gt;{:text=&gt;"Mailbox"}}]</RequiredAttendees>
      </CalendarItem>
    </t:SetItemField>
  </t:Updates>

Note the XML-encoded JSON, rather than the nested XML structure expected.

Would you have any tips? Thanks!