Macro econtext::econtext_function_data

macro_rules! econtext_function_data {
    ($data:expr) => { ... };
}

Provide current function name and some data as context.

Example: `econtext_function_data!(function_argument);'

This has a very low overhead of around 15 ns on a 2020 MacBook Pro.

Unfortunately econtext_function_data! does not support references, so things like &str must be converted into their owned versions, e.g. `econtext_function_data!("file_name", file_name.to_owned());'.