Normalize module names containing multiple objects

[josecelano]

Sometimes single-file and folder module names containing more than one public struct are singular and sometimes plural.

For example:

• src/http/request.rs contains more than one request type.
• src/http/response.rs contains more than one response type.

In general, the plural is the most used option.

The folder name in the plural is better because it contains a collection of that "thing", but sometimes, when you use the namespace, the singular is easier to read, for example:

• request::Announce instead of requests::Announce.

Another advantage of the plural is you do not get Clippy warnings when a function in the module has a suffix which is the mod name, For example, mod handlers and an xxx_handler function inside.

I prefer the plural.

[josecelano]

We can create ADRs like in the Index. And we can start changing it progressively.

[mickvandijke]

Hmm, I dislike using plurals in module names. But when I looked what the Rust std crate uses for the naming convention of modules, I saw that they use a plural name for the std::collections module that includes HashMap, HashSet etc.. So I suppose we should just follow the same plural convention as std then.