Add programmatic API

[epszaw]

fixes #15

This is a basic programmatic API for Allure 3. I don't see any sense in adding more features to it currently because we plan to get rid of CAC due to the many limitations it makes.

Example of the API usage:

import allure from "allure";

allure("run -- npm test");
allure("generate ./allure-results");
allure("awesome --report-name foobar ./allure-results");