Show description of deprecated errors saying why they are deprecated (or unused).

[ericvalcik]

This should resolve Issue #79.

[mukrop]

• The pull request is not denoted as WiP, yet you did not request a review. Is it ready for merge? (I presume so, though I was not sure.)
• Why do you see this solution as bound to OpenSSL? The error_box include is generic – when we have metadata for other libraries, the attributes will have the same names so it should work out of the box. (That precisely is the reason I renamed it from openssl-docs to just docs).
• Related: I now see the renaming of unused to deprecated was probably unfortunate. All deprecated errors are unused, though not all those unused are deprecated. Can you please rename it all back to ununed? (both the attribute and the text description)
• Visually: I would drop the bullet point (actually, the whole bullet list, just make it a <p>). To separate it then from the official docs text, I would suggest typesetting it in italics.

[ericvalcik]

• The pull request is not denoted as WiP, yet you did not request a review. Is it ready for merge? (I presume so, though I was not sure.)

That's my mistake, I forgot to request a review.

• Why do you see this solution as bound to OpenSSL? The error_box include is generic – when we have metadata for other libraries, the attributes will have the same names so it should work out of the box. (That precisely is the reason I renamed it from openssl-docs to just docs).

By being bonded to OpenSSL I meant that this deprecation status is only relevant in OpenSSL. If this error was mapped to an error in another library, the deprecation status wouldn't necessarily mean that it is deprecated in that another library as well. That's why I chose the bullet list approach, so it really shows that deprecation status is only related to OpenSSL. I can see that the commit message is pretty vague about this (also grammatically incorrect), so I'm sorry for that. In the commit message I wanted to stress that I made the deprecation status look bonded to the main library of the error code.