Tag tree

[felko]

Implements #110.

The query command was implemented like this:

neuron query zettel ID
neuron query zettels [TAG]
neuron query tags [TAG] [--tree | --list (default) ]
neuron query --uri URI

The --tree argument provides a JSON tree where each node contains some information that would be useful for a tag browsing feature in editors, as discussed in the PR.

[felko]

Update: The CLI regressed to its previous spec.
Tag queries can only be executed by using neuron query --uri zquery://tags?... for now, and the result is a JSON tree in any way.

The JSON tree follows this format:

tree ::= {
  "tag": reltag,
  "subTags": [reltag...]
}
reltag ::= {
  "name": string
  "exists": boolean,
  "root": string
}

If a zettelkasten contains zettels tagged science/biology and science/math (but not science alone), then the tree for zquery://tags?filter=science/** would look like this:

[
  {
    "tag": {
      "exists": false,
      "name": "science"
    },
    "subTags": [
      {
        "exists": true,
        "root": "science",
        "name": "biology"
      },
      {
        "exists": true,
        "root": "science",
        "name": "math"
      }
    ]
  }
]

This makes it very easy for editors to implement tag browsing, but the format is a little bit complicated, and contains some duplicate information since the leaves will always have exists = true anyway.
The root attribute allows the reconstruction of the "absolute" tag, by doing root/name.

[felko]

Update: The tree is now under this format:

tree ::= {
  "tag": string,
  "count": int,
  "children": [tree...]
}

where count is the number of zettels associated with each tag.

The view has also been updated to display the count.