Py3createtorrent

Changes:

* Fix support for Python 3.7 and earlier. Users have to install the ``typing-extensions`` module, though.
* Attempt to fix the UnicodeEncodeErrors (or similar) that occur when printing files/paths with rare characters that are not
compatible with the console's codec. See 33.

Attempt to fix the UnicodeEncodeErrors (or similar) that occur when printing files/paths with rare characters that are not compatible with the console's codec. See issue 33.

**Changes:**

* added: py3createtorrent **can now be used as a Python module**. This extension was contributed by ToasterUwU.
* changed: the automatic piece size calculation now uses a **larger maximum piece size of 64 MiB** (previously 16 MiB was the maximum).
* changed: **switched to LGPL license** to accomodate usage as a module.
* changed: removed coppersurfer tracker from default config (tracker abbreviations) and also removed all mentions of coppersurfer in the docs. It seems that this tracker has been taken offline a long time ago.
* internal: configured GitHub Workflows for automatic dependency updates and code checks. This was contributed by ToasterUwU.

**Changes:**

* added: **multithreading** for much faster torrent creation (about 30-40% faster). The number of threads can be controlled with the new ``--threads`` option. It defaults to using 4 threads which will be a good choice on most systems.
* added: ``--version`` command
* improved: formatting and content of ``--help`` output

**Changes:**

* fixed: Faulty torrent name and 'name' field when using relative path '.', see 11

**Changes:**

* changed: **requires Python 3.5+ now**
* changed: specifying trackers is now optional with the new ``-t`` switch, thus **trackerless torrents are now
possible**
* added: **bestN shortcut**! It is now possible to add the best N trackers from ngosang/trackerslist (https://github.com/ngosang/trackerslist)
by using the new ``bestN`` shortcut
* changed: use **external JSON files for configuration**, by default try to load ``.py3createtorrent.cfg``
from user's home directory
* added: DHT bootstrap nodes can now be specified with the new ``--node`` switch (doing so is recommended for
trackerless torrents)
* added: **webseed support** with the new ``--webseed`` switch (GetRight style, see http://bittorrent.org/beps/bep_0019.html)
* changed: increased max piece size to 16 MiB
* changed: show warning if piece size is not a multiple of 16 KiB
* changed: updated the default trackers (openbt is now opentrackr, dropped publicbt, added cyberia and coppersurfer)
* added: Pipfile and Pipfile.lock for pipenv support
* added: README.md
* changed: improved performance of single file torrent creation
* fixed: parentheses are now allowed in names specified by using the ``--name`` switch
* refactored: switched to bencode.py module for encoding the torrent data
* refactored: switched from optparse to argparse
* refactored: reformatted code with yapf, using a new column limit of 120
* refactored: added type hints to enable analysis with mypy (we use Python's typing module which was added in
Python 3.5, thus Python 3.5 is the new minimum version that is required)