Update README.md

Reflect the syntax of newer versions of the 'soap' module, and be a bit more verbose in the JS example.
Add dependency on soap module into package.json
Whoops, add missing comma
Specify as a peer dependency
This means "install the soap module with the specified version alongside
marketo-soap-security".  See http://blog.nodejs.org/2013/02/07/peer-dependencies/
Merge pull request #1 from mozz100/master

Specify 'soap' as a peer dependency, and update to use soap 0.2.x