Release 0.5.0

• Uses hiredis (v1.0.0 or later) as an external dependency rather than a builtin part.
• Support for SSL/TLS introduced in Redis 6
• Support for IPv6
• Support authentication using AUTH
• Handle variable number of keys in command EXISTS
• Improved CMake build
• Code style guide (using clang-format)
• Improved testing
• Memory leak corrections and allocation failure handling