More fluent usage of PredicateBuilder in assertions

[topbadger]

Added static helper method and method overloads to make assertions using the PredicateBuilder more fluent.

This allows assertions to be declared as follows:

assertThat(logger).hasLogged(aLog().withLevel(Level.WARN).withMessage("Something"));

as opposed to:

assertThat(logger).hasLogged(new PredicateBuilder().withLevel(Level.WARN).withMessage("Something").build());

[codeclimate]

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