Complete refactor

[auronandace]

I have come to realise that the benefit of a streaming decoder/encoder is that the whole input data doesn't need to be loaded into memory to make progress for decoding/encoding.

Currently, this library requires that the entire input data (QOI image in bytes for the decoder, pixel values in bytes for the encoder) is already fully loaded in memory and the input data fed into the decoder/encoder is simply a slice pointing to where it is stored. This effectively nullifies the main advantage of making this library a streaming decoder/encoder.

This entire library needs to be refactored to allow feeding a series of bytes that represent incomplete data to the decoder/encoder. Then it will truly be a streaming decoder/encoder library.

I have some ideas on how to accomplish this which should make the library difficult to misuse.