Macro loggy::is_an_error

macro_rules! is_an_error {
    ($default:expr) => { ... };
}

Provide program-wide control over whether some note(s) are considered to be an error.

This is typically invoked as pub mod foo { is_an_error!(true /* or false */); }.

This will define a nested module which exposes the following:

• pub fn is_an_error() -> bool returns whether the event is considered to be an error. This is initialized to the value passed to the macro.

  This is intended to be used in note!(foo::is_an_error(), ...), using the note! macro provided by loggy. It will behave as either an error! or a warn! depending on the value.

• pub fn set_is_an_error(new_value: bool) -> bool sets whether the event is considered to be an error, returning the old value for convenience.

  This allows the program to modify the setting at run-time, for example by parsing the command line arguments. TODO: Provide additional functions to automate this.