add format util to log suite

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/log/fmt.rs

+use std::fmt::Write;
+
+use super::{color, Level};
+use crate::Result;
+
+pub fn html<S>(out: &mut S, level: &Level, span: &str, msg: &str) -> Result<()>
+where
+	S: Write,
+{
+	let color = color::code_tag(level);
+	let level = level.as_str().to_uppercase();
+	write!(
+		out,
+		"<font data-mx-color=\"{color}\"><code>{level:>5}</code></font> <code>{span:<12}</code> <code>{msg}</code><br>"
+	)?;
+
+	Ok(())
+}

src/core/log/mod.rs

 pub mod color;
+pub mod fmt;
 mod reload;
 
 pub use reload::ReloadHandle;