Parse metadata block

[Klafyvel]

The semantics of metadata is not well specified yet, but Vhyrro tells me that right now the tree-sitter parser supports the following:

key:value goes here
key: value~
with a bunch of text
key : value

key: [
   value one
   value2~
   with extra text
   value3
]

key: {
   nested: value
}

array-with-complex-items: [
    [
      value 1
    ]
    {
       more: complex stuff
    }
]

That can be a good start.