Implementing basic SWKStorage

[dimakura]

Features in this PR

• [x] Initalization with size
• [x] Initalization with array
• [x] Subscript opreators
• [x] Deinitialization
• [x] elementSize size of each element

Subtask of #7

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A SWKStorage is collection of Float data type. There are also predefined storages for other primitive data types:

• SWKByteStorage, corresponding to Swift's Int8 type;
• SWKCharStorage, corresponding to Swift's Character type;
• SWKShortStorage, corresponding to Swift's Int16 type;
• SWKIntStorage, corresponding to Swift's Int32 type;
• SWKLongStorage, corresponding to Swift's Int64 type;
• SWKFloatStorage (same as SWKStorage), corresponding to Swift's Float type;
• SWKDoubleStorage, corresponding to Swift's Double type. You don't usually create SWKStorage as it's automatically allocated in tensors. In case you still need to create storage yourself, there are two ways how to do it:

  // 1. Creates uninitialized storage of size 10
  var storage = SWKStorage(10)
  // 2. Creates storage of size 4 with elements initialized from the array
  var storage = SWKStorage([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
  // Some properties of the storage.
  print(storage.size)        // 10 -- number of elements
  print(storage.elementSize) // 4 -- bytes taken by each element
  print(storage[5])          // 6.0 -- value of the 6th element