Re-factored Session() new-up to be compliant with requests-1.0+; Fixed p...

Re-factored Session() new-up to be compliant with requests-1.2.0; Fixed problem with parenthesis nesting in _prepQuery as described here:

http://stackoverflow.com/questions/14675004/rally-pyral-sdk-error-with-a-query-with-more-than-two-terms-error-parsing-expr