adds missing return in isUUIDv3() and isUUIDv4()
changes isUUID() to use pattern.test(str)
adds err msg for isUUIDv3 and isUUIDv4
adds tests for isUUIDv3()
adds tests for isUUIDv4()
Merge pull request #204 from conorgil/master

Fixes isUUIDv3 and isUUIDv4