fix-json-multiline

[MrAmericanMike]

With some help apparently this changes should fix the multiline error I mentioned on #89

This results in a new line that looks like this:

"description": "Remove Mouseover Highlight\\nby MrAmericanMike",

JSON validates. And apparently that how a new line in JSON should look like. https://stackoverflow.com/questions/4253367/how-to-escape-a-json-string-containing-newline-characters-using-javascript

PS: I also moved the pack.mcmeta to use that, as it's technically a json file too, even when it's not using multiline, but I guess it's better just to be safe. And this way if other edge cases need special handling, we should be ready.