Adds + and += operators to dictionary

DictionaryMergeExtension.swift

/// Merges right hand side dictionary into left hand side dictionary. Works on nested dictionaries as well.
///
/// - Parameters:
///   - lhs: Dictionary you want to merge someting.
///   - rhs: Merging dictionary.
/// - Returns: Returns merged dictionary.
internal func +<Key, Value> (lhs: [Key: Value], rhs: [Key: Value]) -> [Key: Value] {
  var result = lhs
  rhs.forEach {
    if let dict = $1 as? [Key: Value] {
      if let exist = result[$0] as? [Key: Value] {
        result[$0] = exist + dict as? Value
      } else {
        result[$0] = dict as? Value
      }
    } else {
      result[$0] = $1
    }
  }
  return result
}

/// Appends the right hand side dictionary. Works on nested dictionaries as well
///
/// - Parameters:
///   - lhs: Dictionary you want to merge someting.
///   - rhs: Merging dictionary.
internal func +=<Key, Value> (lhs: inout [Key: Value], rhs: [Key: Value]) {
  // swiftlint:disable:next shorthand_operator
  lhs = lhs + rhs
}