Use modified utf-8 for encoding and decoding strings

[ch-yx]

https://github.com/vberlier/nbtlib/blob/a6c0cd949e10f189581ca11026a0c600ee298e11/nbtlib/tag.py#L225

[ch-yx]

m-utf8 is used by java....

[vberlier]

I won't be able to do anything about it in the coming weeks but I plan to start making releases for nbtlib v2 around september/october, it's going to be on the list of things that will get fixed with the rewrite.