Busypie

* Allow to use busypie with Python's async/await
* Added Python 3.8 compatibility checks
* Allow to define a custom description of condition
* Now content of lambda is shown on timeout error
* Added description field to ConditionTimeoutError

* Added set_default_timeout function to allow changing timeout default value
* Added reset_defaults function to reset default values

* Allow to ignore specific exceptions with ignore_exceptions
* Allow to change default polling interval with poll_interval
* Allow to start expression with given()
* Allow to change polling delay with poll_delay
* Validate poll delay is smaller that max wait time
* Added validate that time values are positive numbers

* Allow to wait up to specific timeout
* Allow to ignore all exceptions

* Allow to to wait up to specific wait time
* Allow to ignore all exceptions