Grizzled-python

- Added `grizzled.text.stripmargin()` function.
- Converted test framework to `pytest`.

- Added tests for `grizzled.file.includer.Includer`.
- Removed URL support in `grizzled.file.includer.Includer`.

- Updated to support Python 3 _only_. Indeed, it requires Python 3.6 or better.
- Updated API docs to use [pdoc](https://github.com/mitmproxy/pdoc/), instead
of Epydoc
- Removed `grizzled.collections.OrderedDict`. Use the standard Python
`collections.OrderedDict`, instead.
- Removed `grizzled.Configuration`. Use the standard `configparser` classes,
instead. (They lack support for include files, but you can preprocess the
file using `grizzled.file.includer`, if you need that.)
- Removed entire `grizzled.db` package. It's woefully out of date.
- Removed entire `grizzled.net` package. There are better ways to handle
HTTP downloads (e.g., the third-party `requests` package), and the `ftp`
module is out of date.
- Removed `grizzled.io.Zip`. Its sole reason for existence was to allow
extracting the zip into a specified directory, a feature the standard
`zipfile.ZipFile` class didn't support when `Zip` was originally written.
`zipfile.ZipFile.extractall()` now provides that functionality, so
`grizzled.io.Zip` is no longer of any use.
- Removed `grizzled.cmdline` module (a front-end to `optparse`). There are
far better solutions out there now
(such as [click](https://click.palletsprojects.com/en/7.x/)).
- Removed `grizzled.exception` module. It's become obsolete.
- Removed `grizzled.history`. Just use the standard `readline` module.
- Removed `grizzled.decorators.abstract`. Use the facilities in the
standard `abc` package.
- Removed `grizzled.file.copy_recursively()`. It was just a single-line wrapper
around `shutil.copytree()`.
- Removed `grizzled.os.file_separator()`. Use standard `os.path.sep`, instead.
- Removed `python_version()`, `python_version_string()`, `ensure_version()`
and `python_version_string()` from `grizzled.system`. They're pointless.
Just use `sys.version_info` and tuple comparison.
- Removed `grizzled.system.class_for_name()`. It's not Pythonic.
- Removed `./run-nose.sh` script in favor of a `setup` command
(`python setup.py test`).
- Fixed `grizzled.file.list_recursively()`. It was totally broken.
- Added (some) type annotations.

- Updated `setup.py` and `setup.cfg` to support building a wheel.
- Updated README with instructions on building, installing, and running tests.
- Removed dependency on `enum34` package.
- Added dependency on `backports.tempfile` package, to allow using
`with TemporaryDirectory()` on both Python 3 and Python 2.
- `grizzled.file.eglob` is now lazy, returning a generator, rather than a list.
- Added tests for `grizzled.file.eglob`.

- Additional changes to support Python 3.

- Changed dependency on `enum` to dependency on `enum34`, for compatibility
between Python 2 and Python 3.