Data Loader functions are not intuitive

[ValleyBell]

The current workflow for using DataLoader is:

• File/MemoryLoader Init → create DataLoader object
• DataLoader SetPreloadBytes → set amount of bytes to load when opening the file
• DataLoader Load → "open" the file + load data (limited by SetPreloadBytes)
• [optional] DataLoader Read → load more data
• DataLoader CancelLoading → "close" the file
• DataLoader Deinit → destroy DataLoader object

New API that would be easier to understand (and be similar to what is common):

• File/MemoryLoader Init → create DataLoader object
• DataLoader Open → "open" the file (don't load data)
• DataLoader Read → load data
• DataLoader Close → "close" the file
• DataLoader Deinit → destroy DataLoader object
• [remove DataLoader SetPreloadBytes]