refactoring and fix tests
refactor Gargor::Individual#set_params
fix log
use #shell instead of #system
exceptions
add tests
refactor: as testable functions
fix: prev_count
select_elites returns instance of Gargor::Individuals
fix spec
Gargor::Individual#shell returns exitstatus
fix: gargor
shuffle after populate
Merge branch 'testing-and-refactoring'