Add custom options to expect-expect

[samayer12]

Fixes #154, expect-expect can support custom strings in addition to just expect.

@veritem, I'm not 100% sure that the unit tests for this rule execute as expected. The unit tests worked in my proof-of-concept repo here, but I tried to introduce some breaking changes in the unit tests and noticed they still passed when I ran them locally with this repo's configuration.

[samayer12]

Regarding that unit test issue I encountered, if you update one of the test inputs in expect-expect.test.ts to be:

{
  code: 'test("shows success", () => {' +
  'shouldNotBePassing(true).toBe(true);});',
  options: [
    { 'custom-expressions': ['expectValue', 'mySecondExpression'] }
  ]
}

the test still passed, at least with the way I ran tests locally.

[veritem]

I just realized that my tests setup broke!
I really appreciate energy you've put into making this work. Thank you!!!!

PS: I'll release a version with that includes this fix once I figure out why my tests can't run normal.