[v3] Implement new concept exercise `docs` and `typespecs`

[angelikatyborska]

Learning objectives

• @moduledoc
• @doc
• @spec
• defining different possible combinations with |
• defining your own type with @type
• naming arguments in a typespec
• the difference between String.t() and string()
• using atom literals in the typespec is a typical pattern (e.g. {:ok, any()} | {:error, any()})

This exercise should provide a boilerplate with already implemented functions that only need a doc and typespec. The functions should be simple so that the exercise can appear early in the concept tree, e.g. do not use Enum.

Out of scope

Anything that would put this exercise at the end of the concept tree or is not practical for everyday usage, so for example:

• pid(), reference() types
• @callback
• improper lists

Concepts

• docs
• typespecs

Prerequisites

Very likely a lot of different data types, like lists, strings, integers, maybe even maps or structs?

Practice exercises

?

[angelikatyborska]

closed in #693