add string extension for capitalize string

src/modules/string.ts

@@ -0,0 +1,16 @@
+export {};
+
+declare global {
+	// Declarations
+	interface String {
+		/**
+		 * Returns a copy of the string with the first letter capitalized.
+		 */
+		capitalize(): string,
+	}
+}
+
+/** Capitalize definition */
+String.prototype.capitalize = function(this: string) {
+	return this[0].toUpperCase() + this.substring(1);
+};