Add checkBooleanAssertions option to no-ok-equality rule

[bmish]

This adds a new option checkBooleanAssertions to the rule no-ok-equality.

The boolean assertions true/false are very similar to the ok/notOk assertions that are already checked by the rule.

Disallows and autofixes assertions like:

assert.true(foo === 1);
assert.false(foo !== 1);

We can enable the checkBooleanAssertions option by default in the next major release.

Fixes #171.

[coveralls]

Coverage remained the same at 100.0% when pulling 54ec754 on bmish:no-ok-equality-checkBooleanAssertions into 8390fa7 on platinumazure:master.

[platinumazure]

Looks great, thanks for contributing!