Fix about_control_statements

* if, then, else, & unless all behave as 
  expected.  nil is neither true or false.

* unless false == !false, etc.

[#54145663]
Fix about_control_statements koan

* while, times, next and for behave as
  expected

* be careful when looping for = and <= in
  order be sure count is correct with while

* break will jump out of a control structure
  when a condition is met

[#54145663]
Merge pull request #13 from bayendor/54145663_about_control_statements_master

Fix about control statements master

[Delivers #54145663]