Fix Issue #14

Fix Issue #14
Related to https://github.com/prydonius/spinning_cursor/issues/12#issuecomment-20354890

Now we can do like this.
```Ruby
@num = 1
sc = SpinningCursor.setup do
  banner "My banner"
  type :spinner
  delay 0.5
end

sc.start
@num += 1
sc.stop

# Now @num == 2 and the code make it clear that the @num instance variables are the same.
```