Add option to fence tables

[J0hannes101]

Adds an option to wrap tables inside fences
Example:

fn main() {
    let html = r#"
<table>
  <tr><th>Name</th><th>Age</th><th>City</th></tr>
  <tr><td>Alice</td><td>30</td><td>Berlin</td></tr>
  <tr><td>Bob</td><td>25</td><td>Paris</td></tr>
  <tr><td>Charlie</td><td>35</td><td>London</td></tr>
</table>"#;

    let out = config::plain()
        .fence_tables()
        .string_from_read(html.as_bytes(), 50)
        .unwrap();
    println!("{}", out);
}

This makes tables render correctly in Markdown previews:

───────┬───┬──────
Name   │Age│City  
───────┼───┼──────
Alice  │30 │Berlin
───────┼───┼──────
Bob    │25 │Paris 
───────┼───┼──────
Charlie│35 │London
───────┴───┴──────

instead of:
───────┬───┬──────
Name │Age│City
───────┼───┼──────
Alice │30 │Berlin
───────┼───┼──────
Bob │25 │Paris
───────┼───┼──────
Charlie│35 │London
───────┴───┴──────

[jugglerchris]

That's a simple clever idea to improve tables when treating it as markdown with proportional fonts! (The long term answer would be to add an option to use markdown table formatting as an alternative to fixed-width cells)

I wonder if it's slightly too simple, though - nested tables are always a bit tricky, and I guess there would be extra ``` around the inner tables? Either way, would you mind adding a unit test or two checking for the correct output?

[J0hannes101]

I wonder if it's slightly too simple, though - nested tables are always a bit tricky, and I guess there would be extra ``` around the inner tables? Either way, would you mind adding a unit test or two checking for the correct output?

You were right - nested tables added extra ```.
The fix was simply to track the depth of the rendered table and only apply the wrapping on depth 1.
I added tests for both normal and nested tables.

[jugglerchris]

Merged, thanks!