Lemoncheesecake

- tests can now be run in parallel using `lcc run --threads N` command; please note that test suites are run
**sequentially** and that tests within test suites are run in **parallel**, this behavior will be improved
in future releases so that tests can be spread on different threads independently from their parent suite

API breaking changes

- the signature of `pre_run` and `post_run` methods of `ProjectConfiguration` class in user `project.py` file
is now `{pre_run,post_run}(self, cli_args, report_dir)` instead of `{pre_run,post_run}(self, report_dir)`,
in other words: CLI arguments are now passed in pre and post hook methods of the project

- **API**: in 'detached_step' context manager, handle possible exceptions in order to properly caught exceptions
raised within a new thread
- **report**: simplify report check descriptions produced by `check_that_entry` and `check_that_in` functions
- **ReportPortal**: fix various regressions introduced in 0.17.0

- **API**: fix add_test_in_suite and add_tests_in_suite functions missing in `lemoncheesecake.api` module

- **API**: replace `add_test_in_suite` and `add_tests_in_suite` functions by `add_test_in_suite`, this function no
longer modifies the function passed as argument (former functions has been kept and just call the new one,
`before_test` and `after_test` argument are now ignored)
- **API**: add the ability to log into multiple steps at the same time using `set_step(description, detached=True)`,
`end_step(description)` and `detached_step(description)` context manager
- **CLI**: when `--passed` or `--skipped` or `--failed` arguments are passed they imply `--from-report`
with the default report directory
- **report**: improve check description for `all_of` and `any_of` matchers
- **under the hood**: event management refactoring: instead of passing all event related attributes directly to event
handlers, everything is now gather in Event classes
- **under the hood**: for logging report data (steps, logs, checks, ...) the `ReportWriter` no longer maintains a
context to update the `Report` instance, instead, the needed context (report location) is now available in the
Event instances (which is set by the `Runtime` class)

- **CLI**: add three commands: `lcc top-suites`, `lcc top-tests` and `lcc top-steps` to show suites, tests and steps
(respectively) ordered by their duration

- **API**: add `{check,require,assert}_that_in` functions to make match operations on dict easier
- **API**: add `is_true` and `is_false` matchers
- **lcc report**: use default report dir if the command is called without report path argument