Add safe mode option which forces use of blocks with the method calls
Change the SafeModeException to StandardError
Add documentation
change method from safe_mode to safe_mode?
Merge remote-tracking branch 'jduff/add_safe_mode'

* jduff/add_safe_mode:
  change method from safe_mode to safe_mode?
  Add documentation
  Change the SafeModeException to StandardError
  Add safe mode option which forces use of blocks with the method calls

Conflicts:
	test/timecop_test.rb
Fix test (#96)

From http://apidock.com/ruby/Time/nsec:

The lowest digit of to_f and nsec is different because IEEE 754 double is not
accurate enough to represent nanoseconds from the Epoch. The accurate value is
returned by nsec.