Remove abstract on Util class

Forbid instanciation excplicitly with a private constructor.
Add test for forbidden constructor on Util

Trying to instanciate a private constructor generates a Fatal Error
which (I think) cannot really be tested with phpunit.  So instead
changing to use public and rely on Exception. Anywayz
Add test for Util private constructor
Fix code coverage
Remove Util private constructor
Merge pull request #56 from 4d47/on-first-read

Remove abstract on Util class