Bumping clippy and fixing warnings

[tomusdrw]

Notable new checks:

1. Types and variables names in docs has to be wrapped in backticks.
2. Clippy warns about very similar names of variables (which doesn't make sense in couple of cases, like: _lock is very similar to block;))

Other common fixes:

1. Please use map_or and map_or_else instead of chaining map with unwrap_or or unwrap_or_else respectively
2. Don't use .iter() -> & is enough.