Make it easier to find out about array and map literals

[lerno]

The initial parts of the current overview documentation deals with literals: https://odin-lang.org/docs/overview/#lexical-elements-and-literals

However, this section only mentions characters and numbers. It does not mention array literals, which are only implicitly mentioned here: https://odin-lang.org/docs/overview/#fixed-arrays and given an example here: under a different heading: https://odin-lang.org/docs/overview/#slice-literals. Furthermore, I think it might lack some of the ways one can construct array literals.

For maps the situation is similar: https://odin-lang.org/docs/overview/#maps

And furthermore it is not clear if the map initialization also allows you to initialize nested maps, e.g. a map containing a map of ints.

The literals missing from the first part that I have seen are:

1. Array literals
2. Slice literals
3. Map literals

true, false and nil could also be considered literals and should probably be listed as well.

[hasanyasin]

Just taking notes here to use as reference when preparing a PR to resolve this. Please add other things you find missing related to literals.

Considering the less formal style and organization of the document, a good solution would be:

• under the initial literals section that @lerno mentioned, we add a brief note stating that literals for advanced types are explained under their respective sections, possibly with a list of links to each section.
• then we scan all the advanced type sections and make sure we list each accepted literal format/style for every type.

Ranged fields in array literals certainly deserve a paragraph or two with examples.

Another missing piece that I noticed is that there is no mention of struct field tags under struct literals section. However, there is an example of

`fmt:"..."`

later under built-ins section.