Package Control 4.0.0-beta9

Fixes

• workaround for library upgrade/removal failing due to DLLs being locked on Windows OS.
• *.whl files were not being recognized / installed.
• remove python bytecode cache when deleting libraries
• restore executable bit when unzipping files on Linux/MacOS (#1655)
• fix oscrypto downloader not handling 302 redirections

Features

• add support for pre-build packages deployed via GitHub/GitLab releases
• add and improve json schemas for channels/repositories

Changes

• switch from SemVer to PEP440 version scheme to better handle pre-releases
• more relaxed evaluation of repositories by making some release keys optional
• mark various legacy dependencies as built-in for python 3.8 plugin_host
• add name mapping for some legacy dependencies to avoid naming conflicts with official PyPI packages