Dewi-utils

- use type annotations w/o typing module, requires python 3.10+
- add mailer module (create mail from HTML/txt template and send mails)
- add convert_to_snake_case(str) to strings
- use Node.create() in git module

- fix for Python 3.10
- threading: ensure that job_completed() is called even if exception is thrown

- git:
* add is_existing_remote()
* add methods to collect commit details
* run_output has 'strip' param, default True, for one-line outputs
* add RepoCloner and BranchCreator classes (related to dewi-core's projects,
but the code is independent from it)
- add files.python_repo_hash_md5 to have an a checksum
- threading: drop usage of old, obsolete threadpool module, use ThreadPoolExecutor
(under the hood: no interface change)
- rrdtool.writer: use the own threading module instead of threadpool
- relicensed under the terms of Apache License v2.0 similar to dewi_core

- add git.py (Git) with several helper methods, including
context manager wrapping git stash and git stash apply
- fix setup.py's license header
- Python 3.8+ only

- fix files.find_file_recursively to work without specified directory
- fix typos in lithurgical module
- config's convert_to_bool and convert_from_bool methods are public
- add support of passwords in ConfigPage.input()
- works with Python 3.9

- add threading module for threadpool and jobs
- config.IniConfig uses new DictConfigParser, add as_dict() method