Changes from the previous release: ([diff](https://github.com/alphatwirl/alphatwirl/compare/v0.24.2...v0.25.0))
- updated `ResumableDatasetLoop`
- addressed [\57](https://github.com/alphatwirl/alphatwirl/issues/57)
- pickle `reader` before having it start reading data as `SubprocessRunner`,
which is indirectly held by `EventDatasetReader`, becomes unpicklable in
Python 3
- updated `concurrently`
- moved `HTCondorJobSubmitter` from `HTCondorJobSubmitter.py` to
`condor/submitter.py`
- moved `submit_jobs()`, `query_status_for()`, `change_job_priority()`
`terminate_jobs()` from `HTCondorJobSubmitter.py` to `condor/commands.py`
- moved `exec_util.py` to `condor/`
- `TaskPackage`
- made it callable
- moved it to `CommunicationChannel.py`
- stopped importing it to `concurrently`
- removed outdated script `example_submit_htcondor.py`
- updated docstring, tests
- cleaned code