<details> element

[iamsergo]

Framework did not include a <detail> element.

I have fixed it.

[iamsergo]

Usage:

<details>
  <summary>Summary</summary>
  Some information
</details>

[iamsergo]

Note: <details> and <summary> are not supported by ie.

[yegor256]

@iamsergo you are welcome to submit a pull request!