Add documentation retrieval for module's built-in attributes (#233) #305

Job	Run time
mix test (Elixir 1.13.x \| Erlang/OTP 22.x)	1m 17s
mix test (Elixir 1.13.x \| Erlang/OTP 23.x)	1m 21s
mix test (Elixir 1.13.x \| Erlang/OTP 24.x)	1m 34s
mix test (Elixir 1.13.x \| Erlang/OTP 25.x)	1m 28s
mix test (Elixir 1.14.x \| Erlang/OTP 23.x)	1m 31s
mix test (Elixir 1.14.x \| Erlang/OTP 24.x)	1m 22s
mix test (Elixir 1.14.x \| Erlang/OTP 25.x)	1m 26s
mix test (Elixir 1.14.x \| Erlang/OTP 26.x)	1m 21s
mix test (Elixir 1.15.x \| Erlang/OTP 24.x)	1m 23s
mix test (Elixir 1.15.x \| Erlang/OTP 25.x)	1m 35s
mix test (Elixir 1.15.x \| Erlang/OTP 26.x)	1m 0s
static analysis (Elixir 1.15.x \| Erlang/OTP 26.x)	57s
mix test windows (Elixir 1.13.x \| Erlang/OTP 22.x)	2m 7s
mix test windows (Elixir 1.13.x \| Erlang/OTP 23.x)	2m 35s
mix test windows (Elixir 1.13.x \| Erlang/OTP 24.x)	2m 35s
mix test windows (Elixir 1.13.x \| Erlang/OTP 25.x)	2m 21s
mix test windows (Elixir 1.14.x \| Erlang/OTP 23.x)	2m 45s
mix test windows (Elixir 1.14.x \| Erlang/OTP 24.x)	2m 39s
mix test windows (Elixir 1.14.x \| Erlang/OTP 25.x)	3m 14s
mix test windows (Elixir 1.14.x \| Erlang/OTP 26.x)	2m 20s
mix test windows (Elixir 1.15.x \| Erlang/OTP 24.x)	2m 39s
mix test windows (Elixir 1.15.x \| Erlang/OTP 25.x)	4m 11s
mix test windows (Elixir 1.15.x \| Erlang/OTP 26.x)	2m 8s
	45m 49s

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