The is_not_empty() method as more clearly alternative for !is_empty()

[160R]

Add `if x in option` syntax sugar

Currently we use if let Some(x) = option, which works, but is a bit verbose. This will be more ergonomic, because we don’t need pattern matching in most of the times. The same idea already applied in for x in iter syntax, which effectively replaces while let Some(x) = iter.next(). With implementing this, Rust will be more consistent. Also, other std::ops::Try types might be supported. Considering how commonly they are used, code should be easier to read, write, and maintain.