Some cleanup of builder exception handling
Use new class Repeatable instead of OrderedDict to hold nested repeatables
More checks for which decorators are allowed on ConfigBuilder
Removed use of ok() in favor of assert. Pylint is not happy with ok().
Removed use of '@test' decorator -> great test speedup
Removed usage of nosetet + oktest.dummy io in favor of py.test
 - Now requires pytest to run test suite (nosetest is not required, but stil some oktest left)
General test suite cleanup
Implemented freeze() and _user_validate_recursively() on Repeatable -> avoid isinstance calls
Items and Attributes now have 'value' method
Minor required_if cleanup
 - Added test for regular (non conditional attribte check working when required_if is using)
Removed last dependency on oktest
Updated README with pytest requirement instead of nosetest + oktest
Fix: required_if attributes not fully validated forn non instantiated envs
 - More testcases