TheGardener tags should be compliant with mdlint

[bursauxa]

Current situation

All theGardener files must start with a block like this one:

```thegardener
{
  "page" :
     {
        "label":"My little page",
        "description": "This page will tell you a lot of stuff about things"
     }
}
```

Here is some introduction text...

## Now we start with the actual sections

Problems caused by the current situation

A first problem is that the spirit of Markdown is, everything written in a .md file should make sense when read in a plain text editor - clearly this block is markup, not markdown.

A second problem is that this mandatory block raises the following mdlint error:

mdlint > MD041/first-line-heading/first-line-h1: First line in file should be a top level heading

Proposed solution

Replace the block with a first-level heading with identical semantics, but more compact and meaningful when read as part of the document:

# My little page

This page will tell you a lot of stuff about things

Here is some introduction text...

## Now we start with the actual sections

[GeReinhart]

I got your point. Now those values : label and description are stored as meta data of the page.
They are used to generate the left menu, used on the search.

More over, we will add tags in the

```thegardener
{
  "page" :
     {
        "label":"My little page",
        "description": "This page will tell you a lot of stuff about things",
        "tags": ["stuff","things"]
     }
}
```

to improve the search. So we kind of need this block