Remove auto-camelcasing of contact properties

Hi guys --

Thanks for merging the last one!  We've run into an issue with Contacts.  Sending a contact property seems to automatically camelcase the property name.  This is at odds with the Hubspot validations on contact properties, which does not allow you to make a property with any capital letters, and pretty much makes creating a contact impossible.

```
"status"=>"error", 
"message"=>"[{
              "property":"hsPersona",
              "msg":"Property "hsPersona" does not exist",
              "error":"PROPERTY_DOESNT_EXIST"
              }]"
```

Also, we started down the path of updating the specs to reflect this change, but a lot of specs are currently failing.  It looks like 188881a changed how `Connection#url_for` works, and the specs haven't yet been updated.