Bandersnatch

- Fix keep_index_versions by removing symlinks for non normalized_legacy_simple_directory
index.htmnl - `Fixes 262` - Thanks **ipbeegle**
- Version plugin api + allow external plugins + move to setup.cfg - `Fixes ` - Thanks **dwighthubbard**
- Add in support for `[plugins]` config section with deprecation warning till 4.0
- Add a Maintainers guide + Mission Statement to README.md
- Lots of doc fixes - `Fixes 217-222` - Thanks **vinayak-mehta**
- Add last_serial in index.html - `Fixes 141` - Thanks **rene-d**
- Rewrite of FilterReleasePlugin filter function - `Fixes 196` - Thanks **rene-d**

- Make plugins logs less noisy and more stateful (don't initialize multiple times) - `Fixes 134 147 193 195`
- Latest releases plugin always keeps current version - `Fixes 196` - Thanks **rene-d**

- Add latest version and specific platform plugins - `Fixes 49` - Thanks **rene-d**
- Generate data-requires-python attributes in index.html - `Fixes 68` - Thanks **z4yx**
- Make package filtering logging less noisy when disabled - `Fixes 146`
- Many pyup.io dependency upgrades

- Change plugins to be off unless explicitly enabled via configuration - `Fixes 142`
- Change all path interactions to use **Pathlib** for more Windows support - `Addresses 23`
- Add a MacOS CI Run with azure pipelines
- Move test_runner from shell to Python for Windows - `Addresses 23`
- More testing improvements and refactor for verify.py
- We now have a reference Docker file + runner.py - `Fixes 113`
- Many pyup.io dependency upgrades

Known Bug

- From 3.0.0 we've been implicitly turning on *ALL* plugins - This version reverses that

- Print help message when no arguments given to bandersnatch - Thanks **GreatBahram**
- aiohttp >= 3.5.0 test and we no longer have `.netrc` error message

- Load default config or passed in config file only *(not both)* - `Fixes 95` - Thanks **GreatBahram**
- Add `--force-check` to mirror to enable full PyPI Syncs - `Fixes 97` - Thanks **GreatBahram**