RFC: Test runner integration

[krzkaczor]

Description

Some advanced features like:

• expect a number of assertions
• snapshots

require that earl has some level of integration with a test runner. Such integration can provide:

• hooks before/after test case
• provides a name for a test case

Test runner agnostism

Even though earl should be runner agnostic we optimize for mocha and this should be the first properly supported test runner.

Integration should be as simple as adding earljs/runners/mocha to require option of mocha.

Implementation plan

Good MVP is support for jest's expect.assertions(number). To support this we need post test case hooks. Integration should work with mocha parallel mode.

Old outdated issue: #14