Replace keyword with concrete keyword lists in specs

[lukaszsamson]

This PR:

• Replaces keyword/term with concrete keyword lists in specs for all functions taking options argument
• Adds missing documentation for some of the supported options
• Adds specs for functions with options argument

Rationale:

• Better LSP completions. ElixirLS is able to parse specs and provide completions for keyword options
• Dialyzer validation
• Easier machine transformation to elixir type annotation
• Better consistency. A big part of the API surface already had typed keyword lists.

I originally planned to do this only for public functions, but I realized that it would be better to do it for all functions taking options argument. Some of the internal ones were already documented or had specs.