Missing documentation about HasMoreOutput and NeedsMoreInput

[peckpeck]

What should the caller do when decompress returns NeedsMoreInput or HasMoreOutput ?

1. In the case of NeedsMoreInput, I guess it should call decompress again with the next input and an adjusted out_pos (and same DecompressorOxide)
2. In the case of HasMoreOutput, I don't know if it should call decompress with no input or with the next input, probably with an adjusted out_pos

[peckpeck]

My last PR has added some documentation here https://github.com/Frommi/miniz_oxide/blob/master/miniz_oxide/src/inflate/core.rs#L14

[peckpeck]

In fact answers to this is explained in the discussion here #24