More features, but problems I'm sure

Hi,

I've been adding more features of the Marketo SOAP API, and while I don't think this is a good pull request, it's the way I've got of communicating with you about these and asking you to look at them and comment. =)

Specifically, we've done slightly different things with sync_lead which will lead to conflict.

And I've changed all the produced XML to use SOAP-ENV and different xmlns links, as specified in the current api docs.

Thoughts?