feat(lang): show expected output for examples

[terrabitz]

Closes #26

This MR includes example output along with the code that generates that output. Given foo.go:

package foo

import "fmt"

func Hello(name string) string {
	return fmt.Sprintf("Hello %s!", name)
}

and foo_test.go:

package foo

import "fmt"

func ExampleHello() {
	fmt.Println(Hello("foo"))
	// Output: Hello foo!
}

the output looks like this:

<details><summary>Example</summary>
<p>

```go
{
	fmt.Println(Hello("foo"))

}
```



Outputs:

```output
Hello foo!
```

</p>
</details>

Note, this MR also includes a go mod tidy. This might overlap with #25, so this can be altered if necessary. Additionally, I ended up using the markdown code fence type output as a descriptor, but I don't know if there's a better descriptor to use here.

[terrabitz]

@princjef This should be ready to merge. I don't know why the pipeline's failing, but my guess is it's not directly connected to the changes I made.

[princjef]

Nice change :) As long as we can make the output look reasonable for examples with no output I'm good with it.

[terrabitz]

Support for empty output has been added. Given the following examples:

func ExampleHello() {
	fmt.Println(Hello("foo"))
	// Output: Hello foo!
}

func ExampleHello_noOutput() {
	_ = Hello("foo")
}

func ExampleHello_comments() {
	_ = Hello("foo")
	// This returns a hello string
}

The output looks like this:

<details><summary>Example</summary>
<p>

```go
{
	fmt.Println(Hello("foo"))

}
```

#### Output

```
Hello foo!
```

</p>
</details>

<details><summary>Example</summary>
<p>

```go
{
	_ = Hello("foo")

}
```

</p>
</details>

<details><summary>Example</summary>
<p>

```go
{
	_ = Hello("foo")
}
```

</p>
</details>

[terrabitz]

@princjef This should be good for another round of review. I have added support for empty outputs, as well as rebased on the latest master branch to avoid merge conflicts.

[terrabitz]

An update has been made to differentiate empty output and no output. Given the following examples:

func ExampleHello_emptyOutput() {
	_ = Hello("foo")
	// Output:
}

func ExampleHello_noOutput() {
	_ = Hello("foo")
}

The output is as follows:

<details><summary>Example</summary>
<p>

```go
{
	_ = Hello("foo")

}
```

#### Output

```

```

</p>
</details>

<details><summary>Example</summary>
<p>

```go
{
	_ = Hello("foo")
}
```

</p>
</details>

[princjef]

Looks great 💯

[princjef]

Looks good to go! Will merge once CI checks have passed