MDS015 code ready

MDS015: blank-line-around-fenced-code

Fenced code blocks must have a blank line before and after.

# Config

Enable:

rules:
  blank-line-around-fenced-code: true

Disable:

rules:
  blank-line-around-fenced-code: false

# Title

Content here.
```go
fmt.Println("hello")
```

# Title

```go
fmt.Println("hello")
```

Content here.

Message	Condition
`fenced code block should be preceded by a blank line`	Previous line is not blank
`fenced code block should be followed by a blank line`	Next line after closing fence is not blank