[feature] add custom syn highlight theme from .tmTheme file

[alexzanderr]

here's a simple example of what I would like, look in the comments

use dbg_pls::{pretty, DebugPls, color};  
  
#[derive(DebugPls, Copy, Clone, Debug)]  
pub struct Demo {  
    foo: i32,  
    bar: &'static str,  
}  
  
fn main() {  
    let mut val = [Demo { foo: 5, bar: "hello" }; 10];  
    val[6].bar = "Hello, world! I am a very long string";  
    
	// to specify a theme file as parameter
	let output = format!("{}", color(&val, "path/to/tmTheme"));  
	println!("{}", output);  
	
	color!(&val, "path/to/tmTheme");  
	
	// and to have a builder pattern to cache the theme load
	// the API doesnt need to be like that, you decide
	let colorizer = Colorizer::new().theme("path/to/tmTheme").build();
	// just pass the object as ref
	let colored_string_repr = colorizer.color(&val);
	// just like color! macro
	colorizer.dbg(&val);	
	// this will print module and line information just like dbg!
}

thats all, in short

i just want to be able to load a custom theme.