Change the TypeScript Level type to be a union instead of enum

Fixes #373
Fixes #382

source/index.js

@@ -218,16 +218,4 @@ chalk.supportsColor = stdoutColor;
 chalk.stderr = Chalk({level: stderrColor ? stderrColor.level : 0}); // eslint-disable-line new-cap
 chalk.stderr.supportsColor = stderrColor;
 
-// For TypeScript
-chalk.Level = {
-	None: 0,
-	Basic: 1,
-	Ansi256: 2,
-	TrueColor: 3,
-	0: 'None',
-	1: 'Basic',
-	2: 'Ansi256',
-	3: 'TrueColor'
-};
-
 module.exports = chalk;