add method for toggling parameters
rename 'is_parameter_set' to 'is_position_set'
add 'get_parameter_position' function
add 'is_parameter_set' function
add 'get_rules' and 'get_actual_rules' functions
add 'is_parameter_locked' function
check if parameter can be toggled
refactor 'is_parameter_locked' into 'get_parameter_lockers'
Make 'LockedParameterException' more informative
process side effects when toggling parameters
refactor 'toggle_parameter'
extract tests for 'toggle_parameter' into separate test case
extract base test case
extract 'toggle_parameter_raw'
change order of functions
implement difficulty auto correct
add missing difficulty validation for parameter toggling
add slack notifications for travis
put 'difficulty' inside 'config' namespace
update readme