Improve documentation

[dimitri-br]

Documentation should be improved in general.

Things like fields for structs and enums should be documented.

An example below:

pub struct HttpServer {
    listener: TcpListener,
    pub routes: Routes,

    /* Hidden parameters */
    read_buffer_size: usize,
}

could become

pub struct HttpServer {
    /// A TCP listener, so we can handle incoming connections
    listener: TcpListener,
    /// The routes that this server will use when serving pages.
    /// See `Routes` for more
    pub routes: Routes,

    /* Hidden parameters */ 
    /// The buffer size for reading requests
    read_buffer_size: usize,
}

Obviously not that exactly, but as a general idea, it should be kinda like that.

As an example, this is what level of documentation should be present.