Move #round to helper module
Add a result helper
Let throughput module return a result class
Fix access of class level attrs
Make #to_h generic
Fix indentation
Refine specs
Let memory module return a result class
Let storage module return a result class
Minor spec refactoring
Let swap module return a result class
Let core module return a result class
Let cpu module return a result class
Let load module return a result class
Rename Throughput#sum to #total
Output total with Throughput#to_h
Let traffic module return a result class
Rename Core module to System
Remove Load#to_i because it's misleading
Update documentation