Release 6.4.0

• Command obfuscate accepts multiple arguments as entry scripts
• Fix restrict mode crash issue for Python3.5~3.8 in 32-bit Windows
• Fix super mode issue: attempted relative import beyond top-level package
• Improve security of restrict mode
• For restrict mode 2, do not protect module attributes for performance
• Add restrict mode 5 to protect globals in functions
• Refine the documentation of restrict mode: https://pyarmor.readthedocs.io/en/latest/mode.html#restrict-mode
• Fix platform centos6.x86_64 not found issue (#312)
• On Linux for command licenses the option --bind-mac supports new format: IfName/MacAddress, for example, eth0/00:28:54:af:28