Add rule to avoid using semicolons

[calda]

Summary

This PR proposes a new rule to avoid using semicolons.

Reasoning

Semicolons are not required at the end of a line, so should be omitted. While you can use semicolons to place two statements on the same line, it is more common and preferred to separate them using a newline instead.

Examples

/// WRONG. Semicolons are not required and can be omitted.
let mercury = planets[0];
let venus = planets[1];
let earth = planets[2];

// WRONG. While you can use semicolons to place multiple statements on a single line,
// it is more common and preferred to separate them using newlines instead.
let mercury = planets[0]; let venus = planets[1]; let earth = planets[2];

// RIGHT
let mercury = planets[0]
let venus = planets[1]
let earth = planets[2]

// WRONG
guard let moon = planet.moon else { completion(nil); return }

// WRONG
guard let moon = planet.moon else { 
  completion(nil); return
}

// RIGHT
guard let moon = planet.moon else { 
  completion(nil)
  return
}

Please react with 👍/👎 if you agree or disagree with this proposal.