Improve readability of annotation syntaxes

Nobody has claimed this yet.

The [method currently used](http://localhost:3000/wiki/annotations/#understanding-this-page) for describing how to use annotations can be easy to understand at times:
`---@type `

And also impossible for mere mortals to understand:
`---@cast [+|-][, [+|-]...]`
`---@overload fun([param: type[, param: type...]]): [return_value[,return_value]]`

There must be a better way to represent these more complex syntaxes while also not using symbols regularly in use (`<`, `>`, `(`, `)`, `[`, `]`, `{`, `}`, `@`, `#`, `-`, `+`, `=`, `:`, `"`, `,`, `.`, `?`). Although now that I have listed some in-use symbols, I realize we really are quite limited. It is hard to explain a syntax that uses many symbols… using symbols.

I'm open to any suggestions on how this can be improved 🙂

Start with the linked annotations/#understanding-this-page page and review the complex syntax examples shown in the issue. The issue does not define a preferred replacement or a clear completion test; done would require an agreed, more readable notation and updated documentation examples.

Written by the indexing model from the issue text.