Feature customizable default cache serializer

[onevcat]

For #1362

[Adobels]

Does it have to be CGFloat? Can't it be a Double as it was?

[Adobels]

compressionQuality might be defined as an enumeration with a default value set to high.
public var compressionQuality: JPEGCompressionLevel = .high

enum JPEGCompressionLevel {
  case custom(Double)
  case max, high, med, low

  var rawValue: Double {
    switch self {
    case .max:
      return 1.0
    case .high:
      return 0.9
    case .med:
      return 0.5
    case .low:
      return 0.2
    case .custom(let customValue):
      return customValue
    }
  }
}

[onevcat]

UIImage receives a CGFloat when converting to JPEG data: https://developer.apple.com/documentation/uikit/uiimage/1624115-jpegdata

So I guess keeping them aligned would reduce the mental pressure of users.

What do you mean by "a Double as it was"? I don't think this value once being a Double anywhere... 😕

[Adobels]

I have made the mistaken assumption about the original type of the compressionQuality property because CoreGraphics library was imported.
Below, updated code proposition.

enum JPEGCompressionLevel {
  case custom(CGFloat)
  case max, high, med, low

  var rawValue: CGFloat {
    switch self {
    case .max:
      return 1.0
    case .high:
      return 0.9
    case .med:
      return 0.5
    case .low:
      return 0.2
    case .custom(let customValue):
      return customValue
    }
  }
}

Example of use:

var cacheSerializer = DefaultCacheSerializer()
cacheSerializer.compressionQuality = .max
cacheSerializer.compressionQuality = .custom(0.8)