Set correct instanceURL in session

Get the serverURL from the SOAP response after authenticating and set
the instanceURL.  This allows you to set the instanceURL to
https://www.salesforce.com/ (or https://test.salesforce.com/ for
sandboxes) when authenticating, and not have to know which instance your
org is on.

This fixes the common "Destination URL not reset" error.
Merge pull request #1 from cwarden/reset-endpoint

Set correct instanceURL in session
add 0.4
Merge branch 'master' of github.com:hiratake55/RForcecom
fixed a bug
added 0.4
added zip
patched
patched