v6.1.0

Code quality and performance improvements from these PRs:

• #13 more efficient evaluation
• #15 simplify client logic
• #16 remove policy factory
• #17 use less embedding in policy implementations
• #18 return pointer fron newConfigRefresher
• #19 simplify configFetcher code slightly
• #20 refactor async code
• #21 avoid internal tests
• #22 more external tests
• #23 preprocess config for evaluation
• #24 restore missed logging messages

Special thanks to @rogpeppe for the contribution and the massive amount of work on these PRs.