Fix wording for assertion failures

[nevadascout]

Some (most) assertion failures give strange "reason" messages. Example:

$this->Assert(false)->Should()->NotBeFalse();

fails for reason:
Failed asserting that false is true

The reason should be:
Failed asserting that false is not false

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As a sidenote to this, the assertions should throw custom exceptions instead of calling PHPUnit's base asserter.

Example failure message

FluentAssertionException: expected true to be false because false is falsey"

(Custom reason provided starting at because)

[nevadascout]

Throwing exceptions also allows us to do internal reverse testing.

We'll be able to check that a test fails instead of trying to test every other possible combination.