Merge pull request #23 from atopuzov/master

Implement some new features and fix some bugs
fix for graceful disable of servicegroups
Merge pull request #24 from djinh/master

fix for graceful shutdown of servicegroups
Fixed indentation and excessive spaces
fixed bug with logout() method that caused sessions to remain open in the netscaler.
Merge pull request #26 from codylane/master

fixed bug with logout() method
Fixed NSNitro.login() error reporting

Fixes #27