v0.8.1

• Updated StreamConnection::close() to close persistent connections opened in a previous session to avoid potential issues with re-authentication
• Added metadata keys (Keys::METADATA_FIELD_*) to work with the extended SQL result sets (can be enabled with SET SESSION "sql_full_metadata" = true)
• Removed PHPUnit dependency from example scripts
• Fixed some tests which were failing on MacOS
• Updated test matrix to test against Tarantool 2.5 and 2.6